American Bison: A Natural History 9780520930742

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American Bison

Organisms and Environments HARRY W. GREENE, CONSULTING EDITOR

1.

The View from Bald Hill: Thirty Years in an Arizona Grassland, by Carl E. Bock and Jane H. Bock

2.

Tupai: A Field Study of Bornean Treeshrews, by Louise H. Emmons

3. Singing the Turtles to Sea: The Comcaac (Seri) Art and Science of Reptiles, by Gary Paul Nabhan 4. Amphibians and Reptiles of Baja California, Including Its Pacific Islands and the Islands in the Sea of Cartes, by L. Lee Grismer 5. Lizards: Windows to the Evolution of Diversity, by Eric R. Pianka and Laurie J. Vitt

6. American Bison: A Natural History, by Dale F. Lott

Alllerican Bison . -

Dale F. Lott WITH A FOREWORD BY HARRY W. GREENE

University ofCalifornia Press Berkeley Los Angeles London

University of California Press Berkeley and Los Angeles, California University of California Press, Ltd. London, England First paperback printing 2003 © 2002 by the Regents of the University of California

The photographs showing display hair, display hair loss, copulation, and ejaculation originally appeared in Zeitschrijt fUr Tierpsychologie 49 (1979) and 56 (1981) and are reprinted by the kind permission of

Blackwell Wissenschafts-Verlag Berlin, GmbH. Library of Congress Cataloging-in-Publication Data Lott, Dale F. American bison: a na tural history / Dale F. Lott ; with a foreword by Harry W. Greene. p. cm. - (Organisms and environments; 6) Includes bibliographical references (p. ) and index. ISBN 978-0-520-24062-9 (pbk: alk. paper) 1. American bison. I. TItle. n. Series. QL737.U53 L68 2002 599· 64'3--dC21 2002000243 Manufactured in the United States of America 10

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The paper used in this publication is both acid-free and totally chlorine-free (TCF). It meets the minimum requirements of ANSI/ NlSO Z 39.48-1992 (R 1997) (Permanence ofPaper).

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Contents

Plates follow page 48 Maps are on pages 71 and 169 Foreword, by Harry W. Greene / ix Preface / xiii PART ONE: RELATIONSHIPS, RELATIONSHIPS

1.

Bull to Bull and Cow to Bull /5

2.

Cow to Cow /23

3. Cow to Calf / 28 PART TWO: THE MACHINERY OF A BISON'S LIFE

4. Bison Athletics / 41 5. Digestion: Grass to Gas and Chips / 47

6. Temperature Control/53 PART THREE: WHENCE THEY CAME FORTH. AND HOW MUCH THEY MULTIPLIED

7. Ancestors and Relatives /61 8. How Many? The Bison Population in Primitive America / 69

PART FOUR: THE BISON'S NEIGHBORHOOD

9. The Central Grassland: Where Buffalo Roam When They're at Home /81 PART FIVE: THE BISON'S NEIGHBORS

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Wolves and Bison: Myths and Realities / 99

11.

Buffalo Birds / 105

12.

Diseases and Parasites / 108

13. Pronghorn / 120 14. Prairie Dogs / 12 7

15. Badgers / 133

16. Coyotes / 138 17. Grizzlies / 141 18. Ferrets / 145 PART SIX: HUMAN AND BUFFALO

19. Close Encounters of the Buffalo Kind /151 20.

To Kill a Bison / 158

21.

Bison Numbers Before the Great Slaughter / 167

22.

Where Have All the Bison Gone? /170

23. Attitudes /180 24. Conservation: Then and Now / 185

25. A Great Plains Park /202 Notes /205 Bibliography / 213 Index / 223

Foreword Harry W Greene

American Bison: A Natural History is the sixth volume in the University of California Press series on organisms and environments. Our unifying themes are the diversity of plants and animals, the ways in which they interact with each other and with their surroundings, and the broader implications of those relationships for science and society. We seek books that promote unusual, even unexpected connections among seemingly disparate topics, and we want to encourage projects that are distinguished by the unique perspectives and talents of their authors. Other volumes thus far have concerned the ecology of Arizona grasslands, the behavior of Bornean treeshrews, Seri ethnoherpetology, the amphibians and reptiles of Baja California, and global lizard biology. Among all living mammals, bison are perhaps most emblematic of North America and of the fate of wildlife on a continent so long and dramatically transformed, especially under the weight of our impact. Dur-

ing their most recent twenty thousand years or so, bison have witnessed glaciers advancing and receding with widespread climate changes, invasions of the New World by humans from Asia and Europe, and the extinction of several dozen species of other large mammals. Over those same millennia we have slaughtered bison in numbers beyond comprehension, as men first with spears chased them over cliffs, then later with bow and arrows dispatched them from horseback, and finally with rifles shot them from railway cars. Today bison still roam North American prairies, most of them in a few small herds from Canada to Oklahoma, and their biology still mirrors the seasonal rhythms of weather and local ecology. And as did their Pleistocene ancestors, these massive, shaggy creatures stir up the insects that cowbirds eat, crop vast expanses of grassland, and create vernal pools with their dust wallows. Meanwhile, bison are threatened

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by ever-shrinking habitat, political controversies, and, perhaps surprisingly, the possibility of extinction through domestication. Ask professional animal behaviorists what motivates their field studies and the commonest answer is likely "curiosity," especially a desire to know what it is like to be a particular animal. Although some biologists and philosophers regard that question as fundamentally unanswerable, many of us just as stubbornly find it irresistible, and there's no denying that accurate observations provide windows into the lives of other organisms. Thoroughly documented field biology also supplies the facts that underlie conservation, management, and public concern for nature. American Bison serves all of these goals as it follows one man's lifetime obsession with the details of bison natural history. Dale Lott is a respected scholar as well as a keen and sympathetic observer of animals and people, and I think he must love bison. Lott grew up among these creatures he often as not calls buffalo, and his engaging prose crackles, almost rumbles at times with a deep appreciation for them and their surroundings. Beyond the basic findings of science, he offers pithy comments on rural lifestyles and just enough personal background to give the reader a welcome familiarity and confidence in his views. Perhaps most intriguingly, Lott asks us to distinguish between real and mythical bison, between the animals as they were and still might be and the animals as we wish they were. With honest knowledge, he seems to imply, we might better ask what kind of bison we will tolerate and what kind of world we can share. American Bison comprehensively summarizes the biology of these large mammals. Thanks to Lott's interest in seemingly everything having to do with the Great Plains, along the way we learn about mountains, rain shadows, wind, soil, wolves, prairie dogs, horses, symbiotic gut bacteria, and diseases of cattle. He also tutors us in the basics of ecological theory and behavioral endocrinology, as well as in what to do when a bison cow charges. This wonderful book is packed with facts, some familiar, others new and even surprising. For example, there are likely no more than 30 million bison at peak abundance in North America, rather than 60 or 70 million as is often stated. Ironically, all the founder animals of today's public herds-except for those in Yellowstone and the wood bison in Canada-eame from the stock of famed Texas rancher Charles Goodnight

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and other private owners. Badgers and coyotes sometimes do hunt collaboratively, as long claimed by Indians; and however awkward a grown bison might look to us, one bull did a standing high jump that landed him six feet above his launch site, and another "hopped" an eight-foot-wide cattle guard! We are so fortunate that today there are places in North America to experience such magnificent creatures and that Dale Lotl's life's work inspires us to learn what it's like to be one of them. In the parks and refuges where bison still live freely, a visitor can stand near a herd during mating season and feel the tremble of their movements and vocalizations, or watch a ton of woolly brown herbivore casually drop to the ground and roll in a cloud of dust. American Bison: A Natural History closes with carefully reasoned arguments for a Great Plains Park, a place where we can preserve these animals and thereby save some wilderness for all of us.

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Preface

I had the great good luck to live the first six years of my life in a place where buffalo were the animals I saw most often-the National Bison Range in western Montana. My mother's father was the Range superintendent; my father was a Range employee who had grown up near the Range and had married the boss's daughter. My older brother and I lived on the Range with them in staff housing. When I was ten my parents bought my father's father's farm/ranch three miles from the Bison Range. Through my adolescence the bison herds were visible as dark patches on distant hills, though we occasionally went to the Range to see them up close. College, the army, a Ph.D. in psychology followed by a postdoc at the Institute for Animal Behavior in Rutgers-and I was a thirty-year-old, newly hired assistant professor at the University of California at Davis looking for a suitable subject for field research. Bison came to mind. There were good scientific reasons. Their behavior was not yet thoroughly described and was scarcely analyzed at all. They are easy to see in the grasslands they frequent and are active during the day. Then too, I really liked them-always had. I stopped by the Bison Range on my way from New Jersey to California and began to collect data. I first encountered bison not as symbols of the West, the squandering of a natural resource, or a conservation triumph. They were simply the animals I had seen most often when I was a young child-enthralling in and of themselves. I still see them that way, and my research goal was to know and understand them better. The basic question has always been, how do they get on in the world? This is, to use a couple of very old-fashioned terms, a natural history of buffalo. After years of living near them, and still more years of doing

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field research on them, I'm still fascinated by bison and hope to share some of the magic of my experiences and the things I learned-things about bison and the ecological community they evolved to be a part of. Eventually, people made themselves a part of that community. Their role in it, and in the fate of the bison, must be told too. Animals conduct transactions with their environment, and especially with the other members of their community, primarily through their behavior. Consequently, understanding behavior is fundamental to understanding both the animals and their interactions. I'm happy about that, because I find animal behavior in general fully as fascinating as I find bison behavior in particular. It's hard to imagine-as you fly above mile after mile of corn, soybeans, and cattle feedlots or drive between them-but before East Africa became safari land, rich adventurers went on safari on the Great Plains. Buffalo Bill got his start in show business by laying on a safari for the Czarevitch of Russia-the Grand Duke Alexis. The Great Plains was a good choice. This vast, little-disturbed natural community covered a third of the United States-ereating wonder, inviting adventure. Part of the appeal was the exotic indigenous people, but the main attraction was a sea of grass inhabited by an assemblage of animals mostly unknown elsewhere, and dominated by enormous herds of buffalo. This community no longer exists anywhere, though nearly all the parts have been saved, most in tiny remnants. From a wildlife biologist's perspective, the buffalo was a keystone species-a pivotal figure in an abundant and extensive, but relatively simple, community with direct or indirect links to most if not all the members. I've tried to sketch a picture, using the bison as the focal point, of the scene that filled that vast space. Today we can see it only in our minds' eye, and that's hard. I hope this book makes the task a little easier. I've given a lot of thought to whether I should call my protagonist bison or buffalo. My scientist side is drawn to bison. It is scientifically correct and precise. One kind of buffalo is native to Asia and another is native to Africa; none is native to North America. Yet the side of me that grew up American is drawn to buffalo-the name by which most Americans have long known it. I decided to use both names: bison, or to be exact Bison

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PREFACE

bison, places the animal precisely among the world's mammals, while buffalo honors its long, intense, and dramatic relationship with the peoples of North America. One of the lessons thirty-five years of teaching has taught me is that people usually would rather hear a story than listen to a lecture. The buffalo and each member of the community that buffalo are part of have a story. They're great stories, and it's a pleasure and a privilege to be able to tell them. Some readers will want to pursue some of these stories further. To help them I have placed notes at the back of the book. No superscript appears in the text, but each note Oabeled by page number) references a fact or idea, then briefly identifies a source for more information. Full citations are given in the bibliography that follows the notes. This approach also allows me to give credit to at least a few of the many people whose work has made it possible for me to tell these stories. My research was supported financially by the National Geographic Society, the National Institute of Mental Health, and the University of California Experiment Station. Many people gave generously of their time and talent to help me learn about bison and write this book about them. My research on the National Bison Range was facilitated by Joe Mazzoni and Marvin Kasche and their staffs, while my research on Catalina Island was facilitated by Doug Propst and his staff. The rewriting of my early drafts was made both much easier and much better by the deep, detailed, and tactfully delivered critiques of my fellow members of the VC Davis Nature Writer's Group-Margaret Eldred, Eric Schroeder, and Kelly Stewart. My colleagues Ben and Lynette Hart, Christine Maher, Tim Caro, Donald Owings, Dirk van Vuren, and Louis Botsford read or discussed specific chapters. Jim Shaw and an anonymous reviewer read the entire manuscript. All provided useful information, insight, and perspective. I took all the photographs except figure 34, which portrays my grandfather and a white buffalo calf; that photograph was taken by my mother, Joyce Lott. My editors, Doris Kretschmer and Dore Brown, and their colleagues at VC Press, Karla Nielsen and Nola Burger, encouraged me, guided me, and helped me through the process of turning the manuscript into a boo~-making

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PREFACE

it a better book at the same time. Alice Falk's copyediting of the manuscript was superb. My wife, Laura, put up with the forgotten household duties, the distractible spouse, and the slipping-sliding piles of books and sheets of paper here and there that my writing always entails. To all those named above, and to the many more I cannot acknowledge, my heartfelt thanks.

xvi

Relationships, Relationships

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Bison are gregarious mammals. Each gregarious mammal has a lot of relationships. This section is abou t bison relationships - zvhat they are, how they're expressed, what they do for bison, and how the animals manage them. When Ifirst approached bison as a behavioral ecologist, I was in no position to appreciate any subtlety in their behavior. The scientific descriptions of their communication were still very sketchy. Eventually I would fill in some of those gaps. In the meantime the gaps were often frustrating. Yet at the same time it was refreshing, and in some ways more exciting, to be starting with a nearly blank slate. It allowed me-forced me, in fact - to experience the behavior of bison directly, not filtered by any expectations beyond a very general understanding of the social and ecological demands and opportunities of being a big plant-eating mammal in temperate North America. Perhaps that's why some of my most vivid memories are of scenes I saw those first summers and springs, and of the thoughts that ran through my mind as I took them in. At that tinle I experienced bison social interactions primarily as a grand but largely incomprehensible spectacle, like an opera sung in Italian. I relished the stage, the performers' bigger-than-life presence, the power and purity of their voices. Then, during my first field seasons, I got a rough grasp of bison communication. That allowed me to view scenes at another level-as decoded communicatory behavior creating a rich layer of meaning on top of zvhat I observed. It became like

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RELATIONSHIPS

watching an Italian opera with translated lyrics projected as supertitles above the stage. You understand the plot much better, though the distraction of reading the text takes a bit of the edge off your appreciation of the stage and voices. I've tried to convey some of the drama of bison social behavior in afew scenes without projecting text above them. But the behavioral ecologist's job, and my passion, is to go beyond rhapsodic appreciation by translating the lyrics so that the story line can emerge. Bison social behavior is too marvelous a tale to go untold. Social life comes down to managing-one could almost say juggling-relationships. For bison the most complex relationships play out during the intense though brief breeding season. Attraction, rejection, acceptance, competition, and cooperation within and between the sexes create vital, compelling, generally short-lived, and shifting relationships. These entangled relationships make one complex story that is told in chapter 1. Chapter 2 describes the simpler, more durable, but equally important relationships cows develop with one another. The final chapter in this section is about the social relationships of calves, especially their relationship with their mother.

4

CHAPTER 1

Bull to Bull and Cow to Bull

The sky really is bigger in Montana-a colossal inverted bowl of vivid blue. In late July and early August, plumes of dust, rising with earthwarmed air from the brown grass and rolling rangeland, ascend into that bowl. The dust makers, a herd of bison on the National Bison Range, are going about their business-breeding; and I am going about mine-observing, recording, and trying to understand their behavior. Most of the dust comes from wallows, shallow pits where the bison have tom away the sod with their horns and where the subsoil, dried by the sun and stirred by hooves and horns, turns to a flourlike dust. Some of the plumes start when threatening bulls paw and roll in these wallows; but most occur when fighting bulls plow the soil with their hooves, or when they slam their heads together and the shock explodes dust from their bodies. Now an old bull bellows. His back arches, his belly lifts, his neck extends, and a sound that seems equal parts lion's roar and thunderclap

booms across the grass. An eighteen-inch scar runs up his ribs. His horn tips, shattered in other battles, are blunted and worn. Fifty yards away his opponent, a six-year-old bull in his p~ime, bellows back, glances at the cow he is tending, then urinates into the dust of a wallow and rolls in it, slamming his 2,000 pounds sideways into the dust. It spurts from beneath him, filling the air around him like the burst of smoke a stage magician vanishes into. The prime bull emerges from this cloud, headed toward the old bull in a menacing walk. His forefeet stamp with each step, making the hair pantaloons on his legs dance and exploding little puffs of dust from his coat. As each front foot stamps, the bull snorts. His tail stands up like a living question mark. It's an impressive display, and from where I sit, in an ancient jeep, an intimidating one. But the old bull is not intimidated. He too

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has wallowed and now advances, matching stamp with stamp, snort with snort. As they grow closer their bellows intensify; they seem to signify pure fury. Most such ch:.~lenges seem to be elaborate tests of the opponent's determination and end without a fight. Most fights involve a cautious locking of horns or hooking uppercuts or shoving head to head, ended when one animal signals submission and the winner lets him go. But this is not a test of determination and it's a different kind of fight-one of those in which the bulls hurl themselves at each other, elongating their bulky bodies into animated battering rams as they launch themselves for the first blow. Their heads come together with a terrific shock. It ripples through their bodies in a visible wave. lance saw a bull somersaulted backward by such a charge: 2,000 pounds of bull flipped upside down like a lawn chair in a gust of wind. Both these bulls hold position after the first shock and dig in for a serious fight. They slam their heads together again. Clumps of hair the size of a fist are caught between their short, heavy, curved horns, then sheared off and tossed into the air. The animals circle, each trying to reach the other's flank with a hooking horn. Both pivot around their forefeet with the speed of featherweight boxers, and each parries the other's seeking horns with his own while their powerful necks absorb some of the force of the impact. Their hair absorbs some too. By the time a bull is six years old, a mat of hair several inches thick extends from the top of his head down across his forehead, thinning gradually until it stops just above his muzzle. His eyes peer from shallow wells, his ears flick out from deep recesses, and the space between his horns is completely filled with this luxuriant growth. Beneath this natural shock absorber, a thick layer of tough hide covers a rock-solid skull. Now the bulls lock horns and push hard, their hooves plowing soil as each tries to drive his opponent back. The old bull is pushed back and a little sideways, dust spurting from beneath his skidding feet. Suddenly a foot catches on a rock and he trips and falls onto his side. It is rare for a helpless bull to be attacked by the winner, but this time it happens. The younger bull strikes down and forward with his horns, slamming them into the old bull's flank and hooking right and left. The curves

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BULL TO BULL AND COW TO BULL

of his horns make most of the contact and deliver bruising, possibly ribbreaking, but not fatal blows. Then the tip of one horn plunges through skin and muscles and into his opponent's abdomen. Only one horn penetrates, and it penetrates only once, but the wound will be mortal. The younger bull ends his attack and returns to his cow. In a few minutes the old bull will rise to walk away. He will graze again, drink again, sleep again. But an infection will send matter oozing down his ribs in a few days, and in a few weeks it will kill him. Yet as one life starts to ebb, another begins. The victorious bull has mated with the cow he was defending and a calf has begun to form. Its birth is the renewal that has made North America bison country for thousands of generations. Siring as many as he can of that calf's generation is the bottom line for each bull, and it's the imperative that justifies their risking their lives in the battles their bodies are built for. But while physical prowess is an essential tool in managing a relationship between two males, it can't be the only tool, and in fact it's one of the least-often used. Much more frequently they use communication, which evolved as a means not to transfer information but to do what attacks do-manage another individual's behavior to one's own benefit. In some relationships honesty is the best policy, and communicating animals transfer real information. A mother hen calling "food here" to her chicks is managing their behavior to their benefit as well as hers by telling the

truth. They get food, and she gets her genes represented in the next generation. On the other hand, young men in a hormone-induced haze who exclaim, "Of course. I love you!" while fumbling with a woman's bra are often lying through their teeth. But both the hen and the men are using signals in fundamentally the same way-to modify another's behavior for their own benefit. It starts with anticipation. A bull's defenses work only if he knows when and where to deploy them-he must anticipate attacks. So the bull must be a seeker-actively scanning or even probing his environment for clues about whether or not he is likely to be attacked. Call it actively anticipating. A territorial animal can predict attack pretty successfully by knowing territorial boundaries. The territory owner usually challenges all com-

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petitors within a given space and keeps up the pressure with threats and attacks until they leave. But bull bison aren't territorial. They are roamers, drifting singly or in small, temporary groups. Because they cannot use their location in space to predict whether or not another animal will attack them, they read the animals around them, detecting and responding to behavior that consistently precedes an attack. Reading it accurately is a second tool for managing relationships. It's clearly to the advantage of an animal about to be attacked to become canny in judging his enemy's behavior. Generally the task is made easier by the opponent, who, instead of disguising the coming attack, often amplifies preattack behaviors, draws attention to them, and in every way makes it easy to see what he is about to do. A bull doesn't just walk toward his opponent: he stamps with each step, setting his foreleg pantaloons dancing, and grunting with each stamp. If forewarned is forearmed, why not attack first and give indication later? The reason, of course, is that it may not be necessary to attack at all. Forewarned may be foredefeated-at least often enough to make the warning worthwhile. Call these forewarnings threats. A fight avoided is also risk and energy expenditure avoided. Fighting is an occasionally necessary grand spectacle, but the real biological drama lies in the complex, drawn-out, and frequently subtle ways in which most conflicts are settled by communication. Bulls do most of their communicating during the breeding seasonthe only time during the year that mature bulls and cows are together for any length of time. The bulls have been alone or in small, temporary groups. Now they join the cows, which have been living in larger groups with the calves and young bulls. The bulls seek out cows about to breed and stay with them (they "tend" them), keeping other bulls away by threatening and fighting. But threatening and fighting are also common between bulls that are not defending cows. Since receptive cows are the only scarce resource in the bull's economy, this seems surprising at first: one wonders what the nontending bulls are fighting about. But a rival dominated now will probably give way later without a contest, saving a tending bull time and energy when he has none to spare. Not that the bull works it all out in this

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BULL TO BULL AND COW TO BULL

fashion. He simply has a powerful urge to dominate other bulls, and following this impulse works to his advantage. The drive to dominate is so powerful that it occasionally interferes with his real business and its ultimate function-bulls will sometimes leave a receptive cow to threaten a distant bull. Virtually all of us air-breathing vertebrates have found ways to turn our exhalations into communications, and most interactions between bulls start with a sound. On a still day a bull's bellow carries for miles. It's a sort of roaring rumble, and if you can't see the bull or don't recognize the sound you may guess it's a thunderstorm. If the competition presses, the bellowing becomes louder, and a quality that is hard to define but somehow easy to recognize-a quality of fury-begins to grow in it. Often one or both bulls will interrupt their bellowing to paw the ground or wallow. Threatening bulls usually do something we don't understand at all: they urinate into a wallow, then roll in the dampened soil. Do they get enough urine on themselves to send a signal? If so, what could they be . signaling? Could they be exposing the opposition to an index of their testosterone level as salient to a bull bison's keen nose as their bulk presented broadside is to his eyes? Or is there another chemical billboard being displayed? As a bull uses up his physical resources during the rut, he eventually begins to metabolize his muscle. The metabolites in his urine will report that chemistry to a sophisticated nose, and the same nose will know when the bull is still burning fat and his muscle is intact. This would be an honest signal of physical condition. The cost of signaling weakness when you are weak would be compensated for by the benefit of signaling strength when you are strong. An intriguing story, but so far 100 percent speculation. Maybe someday we'll know. If the challenge does not end at the wallowing or bellowing stage, the bulls draw closer to each other and begin to posture. There seem to be two distinct postures. In the "head-on threat," which is simply the posture and movement that precedes a charge, the bull moves toward his opponent with his head held slightly to one side. The more slowly the challengers are moving, the farther to the side their heads are held. When they approach nearly straight on, either one bull submits by turning away or

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they bang heads. But when they approach slowly with their heads well to one side, they often stop close to, but not quite touching, each other and "nod-threat." Nod-threatening bulls stand close enough to reach one another; their bodies may form a single straight line or an angle of up to ninety degrees, but in either case they turn their heads aside. From this position they can attack suddenly by hooking a horn into the opponent's head. The hook always starts when the head is close to the ground, the muzzle tucked back. But in the threat itself, the head-low, muzzle-back position is only a brief interruption of a head-high stance: the bulls' heads drop in a matched movement, then swing back up again, still to one side. A hooking attack may start at the bottom of anyone of the down swings, but the opponent never seems to be caught off guard. After a series of such nods one animal may suddenly submit, ending the clash. Nod-threatening takes place most often between bulls that are not tending cows, as does the "broadside threat." A bull in this posture keeps himself broadside to his opponent with his head held a little higher than normal. Usually his back is arched and he is bellowing. If he moves, he does so slowly, in short, stiff steps that keep him broadside to his opponent. Often two bulls will threaten by standing parallel to each other just a few feet apart. Only rarely does this threat lead to a fight. The encounter may be long as threats go, lasting up to a minute or more, but one of the animals almost always submits. The broadside threat and the nod threat emphasize the degree to which the bulls forewarn their opponents. This forewarning is so elaborate that it has become a force in its own right. It goes beyond permitting the prediction of attack: by substituting for attack, it often overpowers the opponent. That function may account for some puzzling aspects of these postures. Why, for example, do the bulls threaten by turning broadside? When turned this way, a bull seems very vulnerable to attack, particularly if the bull he is threatening is facing him. Since all his protection is concentrated at his head, the usual point of attack, a bison bull is easily wounded by a horn thrust from the side. (This danger, by the way, is more apparent than real. In watching thousands of such threats I have seen only one attack on

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BULL TO BULL AND COW TO BULL

a bull turned broadside.) Perhaps the function of the broadside threat is to display the full size and power of the bull, as well as to forewarn the opponent. If the threatening bull makes a big enough impression, he may save himself a fight. The one recurrent note in all these descriptions of fighting and threatening is that they go on until one animal submits. Submission signals have two functions: they enable a bull to withdraw from an encounter without getting into a fight, and they enable a losing bull to end a fight without retreating a long way. There are two questions to ask about bison communicating submission: How do they signal it? Why do the winners accept it? All bison submission signals are variations on a theme: the submitting bull turns away. Sometimes it's a 18o-degree turn followed by a galloping retreat. At other times it's an abbreviated swing of the head and neck to one side. When it involves a go-degree turn, the submitting animal ends up in the same general position as one who is threatening broadside. But it's easy to tell the difference. In submission the bull's head is usually low, muzzle extended as if to graze-and sometimes he does graze-and the bull is silent. Whatever form the submission signal takes, it almost always stops the threats or attack immediately. One day two bulls dramatically demonstrated the power of this signal. They were fighting in a swale below me. The low ground was moist, so the grass was green even in early August. The spurting dust raised by most fights was missing, and the rich contrast between the warm brown of the bulls' coats and the green grass gave the scene a certain tranquillity. But the bulls were fighting in earnest. They slammed their heads together, stepped back a few feet, then drove their foreheads together again so hard that the shock of the impact seemed to pass visibly through their bodies. After three or four such blows, just as they had drawn back and were poised to plunge together again, one of the bulls simply stood in his tracks and swung his head ninety degrees to the right. The winner had already started his forward lunge. His front feet plowed sudden dark furrows in the green grass as he skidded to a stop. His horns could not have been more than eighteen inches from the loser's neck. The two animals stood immobile for a few seconds; then both walked quietly away.

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RELATIONSHIPS

Fights usually stop just that abruptly with the loser just that vulnerable. One more step, one more lunge by the winner, and the loser would be out. But that step is almost never taken. Why does an act of submission change the winner's behavior so profoundly? One is tempted to explain it by analogy to human institutions, to say that bison operate by a set of "rules." Thus the loser is kept from harm by the winner's acquiescence to rules, just as a football player who has been knocked off his feet is protected from further assault by the rules of football. But this kind of analogy between social behavior and social convention obscures rather than clarifies. The rules of football are a social invention based on enlightened self-interest and reciprocity. Players agree to be restrained from some destructive acts, provided that the opposition is similarly restrained. Kicking an opponent in the head when he is down is so dangerous that everyone agrees that it should draw a penalty that gives the other team some advantage in play. This penalty imposed by a specialized group of rule enforcers is the mechanism through which rules control the football players' behavior. There are, however, no reciprocal agreements and no rule enforcers among bison. Each bull's behavior meets his own needs and no other bull's. The only penalties for any action are those assessed by the action itself. At first this seems wrong. How would a winning bull penalize himself by polishing off a loser? In fact, he would be deprived of two precious commodities: time and energy. The breeding season, when most conflicts take place, is limited, and time spent fighting, even a mop-up operation, is time lost from breeding. Fights to the finish would take even more energy, and that's in shorter supply than you might imagine. When you see bulls in the middle of summer, in th~ midst of tall grass and warm sunshine, their good health and nutrition seem assured. But bison are northern animals, one of the most northern of the cattle family. They have adapted to a climate where food is scarce through long winter months. Bulls die during the winter if fall catches them without enough energy stored as body fat. As it is, the breeding season takes a lot of energy. Mature males lose an average of 200 pounds between June and October. If every fight were long and rough

12

BULL TO BULL AND COW TO BULL

and ended in a cross-country chase, bison bulls, winners and losers alike, might well die before spring renewed the plains. Pursuing and destroying the loser would eliminate the need ever to face him again, of course, but that would accomplish little. Bison breed in large groups, with the males moving constantly from one group to another. There are always many more challengers where the last came from. In the final analysis, the winner does not spare his defeated rivals, he spares himself. The prolonged forewarnings, the reluctance to fight, and the generosity to losers are neither the last noble vestiges of chivalry in our time nor nature's way of exhorting humans to live on a higher ethical plane. Rather, they are carefully balanced behavioral adjustments to the social and ecological circumstances in which the competition between bulls evolved.

OLDER AND BOLDER

Picture this: two men, strangers, both sober, are quarreling about which will buy a drink for a young woman who sits on a stool watching. One is old enough to be subjecting strangers to baby pictures of his first grandchild; the other is just old enough to drink legally. One of the men is pushy-escalating from words toward violence; the other is cautious and restrained. Now, if you can, picture this-it's the old guy who is escalat-

ing-shoulders hunched, on ,the balls of his feet, fists clenched, movements abrupt, voice loud and angry, while the young guy is back on his heels, hands held up and open before him, trying to avoid a fight. There's a lot wrong with this picture. It's a rare young man who gets bolder as he gets older. But the ecologists Chris Maher and John Byers have shown this to be the rule in bison. The older they get, the more likely they are to take the risks of combat in order to tend a breedable cow-not because older mature bulls are more likely to win than younger mature bulls, but because they have less to lose. Thereby hangs an intriguing budgeting issue, which might be titled "How to spend your life the way that buys the most descendants." It's an investment program in which your life is your capital and the return is your offspring's offspring. For male bison, producing offspring usually involves conflict. Each such conflict puts their

13

RELATIONSHIPS

lives at risk. A bull bison's optimal investment strategy weighs possible losses against possible gains and decides how much risk is prudent. He's balancing making a killing against getting killed. Now, a male is not going to live forever, so an optimal strategy must be age sensitive. The younger he is, the more time and future opportunities he stands to lose if he dies. So he should invest cautiously when he's young and has more to lose, but more and more boldly as he gets older and has less to lose. Bison behavior tracks this straightforward logic-the old bulls are the bold bulls. But a man finds such budgeting more complicated. For the bull, getting his sperm on the way to the egg is the end of his investment. For a man, it's the beginning. Until the offspring reproduce, the father's investment has not paid off. Human babies don't stand on their own two feet within ten minutes of being born, don't run in two hours, aren't weaned at six months. Children must be fed and protected for years, and fathers can help, thus investing more in each child. As the investment in children grows, so does their value. Once he has children, staying alive to support their development and eventual reproduction and maybe even that of their children's children is a good alternative to risking his life to produce another child he may not live long enough to rear.

Small wonder grandfathers would rather dote than fight, and are more likely to risk their lives to preserve their grandchildren than to win wooing rights to a woman, no matter how fecund. This attention to one's young is called nepotism. Bull bison never engage in it, but human males, whose genetic survival such lofty detachment would threaten, engage in it all the time-occasionally despite a whole body of civil service law invented to thwart their urge to do so. Not only is life a series of trade-offs, but life itself is one of the things that gets traded off. The trade-offs that natural selection selects usually bring all the costs and benefits to bear and therefore favor very different strategies in different kinds of animals. Different strokes work better for different folks.

COW-BULL RELATIONSHIPS

Bison bulls, and many bison watchers, are preoccupied with bulls' relationships to other bulls and with the tools-spectacular and subtle-they

14

BULL TO BULL AND COW TO BULL

use to manage their relationships. But such tools are just the means to a more important end, an essential and showy precursor to what matters most: making calves. Many living things reproduce with neither preliminaries nor fanfare. They just split in two, grow a bud that becomes a new entity, send up a shoot from a root whenever and wherever. They don't need any help, or even cooperation, from another individual. But apart from a few parthenogenic species of fish and lizards, we vertebrates are stuck with sex. That means, at a minimum, two members of the species being at the same place at the same time so eggs can attract sperm and get fertilized in a fertile egg-friendly environment. For some fish the water around the coral reef where they live is plenty good enough. One to hundreds of females get close to one to hundreds of males, each sex releases his or her gametes at the same time, and eggs and sperm find each other and fuse. But for mammals the equivalent of warm seawater is in a female's uterus. The eggs stay there and the sperm have to journey to join them. This journey requires some seriously specialized equipment and some seriously intimate contact. Where this contact occurs isn't very important, but when and with whom matter a lot. Cows, unlike coral reef fish, release one egg at a time. To get that egg fertilized right they need to attract a suitable bull and become willing to mate with him. Neither of these

things is everyday activity for a cow, so she requires substantial changeschanges that make her more attractive to bulls and, eventually, changes that make her willing to breed with one of them. Back to bulls for a moment. The way to a bull's enthusiastic attendance is through his vomernasal organ, a sensory organ found in many mammals; it has an opening in the roof of the mouth. Cows' urine is full of facts about how near ovulation is. The bull's vomernasal organ seems specialized for an analysis of female urine chemistry that provides information on when a female will be ready to breed. But while bulls will joust seriously to get some female urine on their vomernasal organ, I've never noticed that females go out of their way to present it. However, I have many times seen bulls during the rut bring a resting cow to her feet by prodding her belly gently but firmly with a horn. The cows arise, with what I

15

RELATION SH I PS

take to be resignation, and often urinate in a minute or two. The bull thrusts his muzzle into the stream of urine, then elevates his head, upper lip curled, tongue fluttering inside his mouth, his whole demeanor suggesting a gourmet's appreciation of a fine wine. If he goes from lip-curling to tending, the chances are good that the cow will breed sometime that day. There are two phases to a cow's getting-pregnant physiology: she must ovulate and she must become willing to breed-enter estrus. Each phase is the end point of a complex sequence of hormonal events, and chemical traces of these events appear in the cow's urine. Since each sequence takes several days, chemical signposts show up in the cow's urine days in advance. We call the several hours before the cow breeds pre-estrus, and bulls that test the urine of pre-estrous cows are likely to try to spend the next few hours with her. That's not easy to do. Pre-estrous cows become restless-breaking away from a tending bull and running through the herd. A running cow attracts bulls, and a string of them are soon following her just as a tail follows its comet. When she stops they gather and quickly sort out who among the present company gets to stand by his cow. The cow's best shot at having many grandchildren is to have sons that can

claim a cow just as this bull claimed her. If we assume "like father, like son," he is the best candidate in the immediate circle-but the cow may well make him prove it again with another run through the herd. I always interpreted cows' runs as simply what they did at a particular stage of estrus. The zoologist Jerry Wolff thought otherwise, and he gathered data showing that the lower the tending bull's rank, the more likely it was that the tended cow would run. In addition, cows that ran usually ended up with a bull that ranked higher than the one they ran from. It's just possible the urine left by wallowing bulls plays a part in the cows' physiological progress toward ovulation. All bison wallow and frequently sniff at a wallow before rolling in it. The smell of male urine could stimulate ovulation and a breeding frame of mind, as it may do in moose. Of course a cow can ovulate on her own, but not all ovulations are equal. If you're a calf born on an open grassland roamed by predators, the best cover you have is other newborn calves, who may fill the predators' bel-

16

BULL TO BULL AND COW TO BULL

lies before they get to you. The biologist Richard Estes has shown that wildebeest calves born at the height of the calving season, when the African savanna's predators are relatively satiated, are the least likely to be eaten. So using a clue, any clue, that other cows are relying on to time ovulation can improve a particular cow's chances of having grandchildren. We don't know if bull urine helps synchronize cow ovulation but we do know that cow urine launches bull-cow relationships. A pre-estrous cow's chemistry attracts one-year-old bulls as powerfully as the ten-yearolds, and they all vie to tend a pre-estrous cow. Tending pairs are unveiled as the movement of a grazing herd leaves them behind. Study a pair and you will see the cow grazing a bit, looking fretfully toward the increasingly distant herd. A big bull stands beside her, moving to block her when she sets off after the departing herd. He moves like a basketball player staying between a dribbling point guard and the goal. Sometimes she allows him to hold her in place, but "allows" is the operative word. His moves to block her are quick and graceful, but she is still quicker and more graceful. If she stays it's because she has chosen-or at least settled for-him, not because he has chosen her. She may head straight for another tending bull. When Jerry Wolff compared the ranks of the bulls left to those approached, he found the cows were usually approaching a higher ranking bull. That's one of the forms of choice a cow has, and it makes sense for her to be as choosy as she can

manage to be. She will have just one descendant in the next year, and only half its genes will be hers; she should be as fussy as possible about where the others come from. But the bulls usually severely limit the cows' choice. On any given day there are fewer ready-to-breed cows than eager-tobreed bulls in a herd with a natural sex ratio-that is, nearly as many bulls as cows. The bulls use their bull-bull relationships and social tools to allocate this scarce resource. But the cows are not simply passive. Cows seem to be more receptive to older bulls, and that makes sense; winters, battles, disease, and predators have tested them. We don't yet know what cues besides age the cow may use in making her choice. Could all that bellowing make a difference as to which bull is standing beside her when she stops running? Could it work like some birdsongs or frog croaks-a clue to the female about who might be a bet-

17

RELATIONSHIPS

ter mate? The bulls don't seem to be sending a signal-they appear only to bellow to other bulls. They seldom bellow unless they already have a cow, are trying to displace a bull that has one, or are in the midst of a dominance contest. Even so, the cows can't help but hear them, and I have seen them react. One day I watched a closely tended but resistant cow standing quietly beside the tending bull. Her tail was clamped firmly over her vulva, she chewed her cud, her ears lay passively back, and she jumped away from the tending male's attempts to mount. He was bellowing and glowering at a half dozen bulls standing in a semicircle around the tending pair. It was an all-around stalemate. Then another bull broke it. He walked in from directly behind the tending pair, and when he had closed to forty feet he bellowed. The effect was electric. The tending bull left without a backward glance, hurrying to join the semicircle, and the cow, without a backward glance, lifted her head and tail and flicked her ears forward. The new bull continued past the cow, stalking stiffly around the semicircle while the bulls forming it ducked their heads down and away as he passed each of them. As he presented his right side to the semicircle of bulls the cow pressed against his left side, half mounting him every few steps. When he stopped after passing the last deferent bull the cow stepped directly in front of him, lifted her tail and braced herself. He mounted immediately and four or five seconds later her breeding season was successfully concluded. However important bellows may be to a resistant cow, her priorities and behavior change as ovulation approaches. The time of choosing is a period of conflict between the cow and the many courting bulls. The more competitors, the better for her but the worse for him. His earlier behavior minimized the number, hers maximized it. But now their interests coincide, and they must cooperate and collaborate. Often the cow redirects the relationship. Her physiology is changing fast, altering her behavior along with it. Now, instead of breaking into a gallop every time the bull is distracted by a challenger, she follows him, and when he has disposed of the distraction she stands close, perhaps even positions herself in front of him. If he continues to glower round at the competition instead of mounting her, she may announce her readi-

18

BULL TO BULL AND COW TO BULL

ness to breed by licking him or by sticking a horn in his ribs and prying upward-extracting from the bull a grunt, a tuft of hair, and more attention. She may even mount him, and when he begins to mount her she no longer squirts forward like a stepped-on bar of wet soap, but plants her feet and moves her tail to one side. Even so he may half mount, then drop off several times before he catches on and copulates. Bison sex does not involve a lingering mingling of mucous membranes. He clamps his forelegs around her ribs and penetrates with a lunge. The bull almost always ejaculates within five seconds of intromission (I timed it from movies of the event). His last pelvic thrust is driven home by a contraction of his abdominal muscles so strong that it jerks his hind feet forward and completely clear of the ground, making the I,Ioo-pound cow's hindquarters suddenly support an extra ton of buffalo. Brief though the encounter is, it's usually enough for the cow. She staggers under his weight, not infrequently limps for a while afterward, and four times out of five rejects further attempts by this or any other bull to mount her again for the coming twelve months. What a difference five seconds can make! In five seconds the cow is transformed from eager to unavailable. In just five seconds she has gotten everything of value the bull has to offer for the coming year. Only one cow in five-almost always a cow that bred near the end of the breeding season-will stand for another mounting during one breeding season. In fact one is enough. In a well-nourished herd, 85 to 90 percent of the mature cows will bear a calf in the spring. Though she moves a bit gingerly-back arched, tail extended, sometimes limping-she is soon grazing again. Her breeding program is completed, but not the bull's. His season is in stride, and its success depends on two things-being the only bull to fertilize each of the cows he couples with and coupling with as many cows as possible. Just now a dilemma has him on its horns. This cow could be one of the 20 percent that accept another mount. If she is and he has left her to search elsewhere for a fertile field to plow, her second coupling will be with another bull whose sperm will compete with his for the one egg headed for the cow's uterus. If he stays with her, he will be the bull at the second standing and all the sperm will be his. He can ensure this by staying with her (or, as be-

19

RELATIONSHIPS

havioral ecologists say, "sequestering" her). But the longer he stays, the more likely the other cows' dance cards will already be full when he comes courting. Breeding season moves at a spanking pace. I've seen half the cows breed in the peak four days. To be here or to be there, that is the question. The answer is, play the odds. The odds are that a cow that breeds a second time will do so within forty-five minutes of the first encounter. Most bulls play the odds, sequestering the cow for about fortyfive minutes, then moving on, looking for a new relationship. It's enormously taxing. While breeding, bulls lose 10 to 15 percent of their body weight-mostly fat they will dearly miss in the coming winter. But the potential rewards are also enormous. The winning bulls win big. One year I saw one bull breed five cows while others bred none-one-third of the bulls sired two-thirds of the coming spring's calves. Over three years Jerry Wolff saw one bull breed sixteen cows, while another never bred. The biologists Joel Berger and Carol Cunningham followed a herd for four years and saw one bull breed twenty-eight times while others never bred. Breeding season ends with neither a bang nor a whimper, just a fairly rapid decline in the number of tending pairs. And more and more of the bulls drift away to concentrate on providing their complicated digestive system with the fodder it will convert to fat to carry them through the winter. Their interactions change from constant confrontation to nearly invariable tolerance or passive avoidance. They're not looking for any trouble, and, in the two months following the rut, they come to look a lot less like trouble. The magnificent, menacing mass of hair on their forehead and between their horns, the flowing beard, and the dancing pantaloons that gave advancing bulls such presence are gone. Much of the hair between their horns was barbered away-caught between rubbing horns and sheared off during fights. But the rest of that hair, the beard and the pantaloons, simply falls out after the rut ends and before winter starts. Only mature bulls molt this way, not cows and not even young bulls. Perhaps the hair loss is triggered by the stress of the rut-and perhaps instead, or in addition, it de-escalates the tension between the bulls: each benefits by looking less big-male threatening and thus less likely to provoke other mature males to challenge him, a management tool worth hav-

20

BULL TO BULL AND COW TO BULL

ing when your goal is to graze as much and exercise as little as possible. Then, as winter wanes, the beard, the pantaloons, and the hair between the horns regrows and the bull again wears his special combination of parade ground display and battlefield combat dress. He will again be able to deliver or to survive a full gallop charge squarely on his forehead, but still won't if there is any other way to manage his fellow bulls.

BULLS IN SPRING

The midsummer breeding season is full of sound, fury, dust, and danger. But it would be suicidal to try to keep that up all year round. Bull-bull relationships in the other seasons are comparatively understated. In spring the bulls are hurrying to get ready for summer and winter, but they hurry, in good part, by taking it easy. Two old bulls are lying down, resting and ruminating, about thirty feet apart. The nearest other bison are at least a mile away. One bull rises, stretches, and stands, and in a few minutes the other does too. The first to rise approaches the second. At a distance of fifteen feet, a little tension develops. Their bodies stiffen slightly, and their tails, which had been discouraging flies by flicking from side to side, become still. The bulls look carefully at each other, then slowly relax. They lick their own noses, sending their tongues into first one broad nostril, then the other. They amble off companionably for a hundred yards, grazing as they go, then lie down again. In the summer, in the breeding season, they will be competitors. They may be locked in combat, even mortal combat. But this is no time to quarrel. This is a time to put on fat against the demands of the breeding season in summer and of the cold winter that will soon follow. Not all animals, not even all hoofed animals, must obey this imperative to get fat once a year. Neither the African buffalo nor the Asian buffalo ever get very fat. The seventy species of African antelope don't either, but they don't have to contend with winter. Most animals that do, like the bison, live according to a "fat economy." This strategy simply means that the animal builds up (saves) a store of fat when food is abundant, then lives off it when food is scarce. Both black

21

RELATIONSHIPS

and grizzly bears are archetypal fat economy animals; they pile up fat during a few frantic months of gluttony, then hibernate during the winter, resting cool and even comatose while life is sustained by a store of fat melting slowly like a candle's wax. Storing and using fat is somewhat inefficient. Converting digested food to fat uses some of the food's energy, and converting it back to usable energy requires still more. But what the process lacks in efficiency it makes up in reliability. It makes it possible to survive lean times like the hard winters that always lie ahead of bison. Spring is the time of year for fat economy animals to eat. Not only are their fat stores depleted, but the chance of replacing them is best then. Fat is stored energy, and for most living things energy ultimately comes from the sun. Plants convert the sun's energy into a form plant eaters can use. Though plants are stationary, they too are in a race, a race to have the most surviving seeds or stolons. And so they grow aggressively, sometimes with their greater size depriving their neighbors of sun or water. To the herbivores these weapons are the means to get fat. In the spring plants are not only abundant but also especially nutritious. Growing grass and the flowers, seeds, and other reproductive organs of plants are rich in protein, a critical nutrient that is generally scarce in grass. So now, as the energy from the sun increases day by day, primary production surges and the bison can get fat. And so today the two old bulls move on, grazing, resting, ruminating, and grazing again. Tomorrow both may be all alone and miles apart, or one or both may have joined three or four others; but wherever they are and whoever their companions, they will be grazing, resting, and ruminating: making fat while the sun shines. Their slow pace and laid-back social behavior are their way of hurrying, the fastest way to their goalfat stores.

22

CHAPTER 2

Cow to COW

DOMINANCE RELATIONS

Buffalo cows often seem as contented as the legendary Elsie. A small group grazes green grass, tails swinging languidly; heads nod gently each time a mouthful of grass is clamped between lower teeth and upper hard palate, then torn free with a little jerk. The group moves together, heads all pointing the same way, one cow or another pausing to lick a ticklish rib and look around, a few feet from the cow to the left, a foot or two further from or closer to the one to the right. Serenity personified-with big eyes and small horns. Well, why not. Bulls have to compete to mate, cows don't. Cows need grass to eat, water to drink, companions as a buffer against predators. But food can be in short supply. Whenever a resource is, as ecologists say, "limiting," it's worth contesting, and a social system that allocates that resource will emerge via natural selection. It wouldn't pay for cows to defend territories, so we should look hard for a domi-

nance type of social system. After the roaring, thundering battles of the bulls, the conflicts of cows seem mellow and understated. For one thing, aggression at the level of head banging is rare. The zoologist Alan Rutberg kept count of cow disputes on the National Bison Range. Let watching two cows for one hour equal two cow-hours. In some 26,000 cow-hours, he saw three fights (horn clashes) and one broadside threat. In some 6,000 bull-hours during one breeding season there, I saw 123 fights. Even when they're getting serious, cows' clashes can seem more comic than cosmic. I've seen cows urinate thousands of times and wallow thousands of times, but only once have I seen a cow put urinating and wallowing together as a threatening bull would do. It wasn't breeding season. A cow group was grazing quietly when a lone cow walked up and started to join it. One of the oldest

23

RELATIONSHIPS

cows walked out to meet her, pawed in a wallow, then urinated and wallowed. Her sequence was just like a bull's, but her geometry directed the urine to the grass behind the wallow, while the wallow and the wallower remained perfectly dry. The old cow's belligerence kept the would-be joiner at bay for perhaps fifteen minutes; then she went back to grazing while the newcomer quietly joined in. Although the old cow's urination-wallow was a touch comical, dominance relationships between the cows are no laughing matter. While there's very little violence, there's lots more subtle action. Alan counted aggressive interactions and saw two per cow-hour, ranging from a subordinate withdrawing to a dominant swinging her horns or lunging. The cows are under social pressure, expressed in the physical and social distance between neighbors. As is so often true of participants in relationships, they want to be close, but not too close. The closer a cow's neighbors, the less the danger from wolves but the more the competition-for food, wallows, and water. Being close takes a lot of fine-tuning. Every step brings you closer or takes you farther away from several others, all of whom are also fine-tuning the distance they are from you. Physically, a buffalo cow just plods across ground and through air. But socially, it's as though the air between each two cows were contained in transparent bags that compress and expand as each animal moves closer to or farther from a neighbor. The pressure inside the bags depends on the relationship between a cow and each of her neighbors; and since the relationship is not symmetrical, the pressure of the "same" bag is different for each of the cows. The dominant member of a pair may feel a little pressure when stepping toward her neighbor, while the subordinate may feel intense pressure when stepping toward the dominant, and not move as far. In addition, the cows can vary that stable, baseline pressure. A deferential head duck by the subordinate decreases the pressure for both; a threatening head swing by the dominant raises the pressure for the subordinate. The cows aren't seeking an absence of pressure. If they can't feel any there they find somebody. And up to an optimal point, the more pressures they can feel the better. Being a dominant member of a group has high potential payoff. Alan Rutberg broke the process of feeding into two parts: searching and har-

24

COW TO COW

vesting. In Yellowstone Park, subordinates searched more and harvested less than dominants. Feast and famine were regular visitors to the Great Plains, with wet weather in some years and drought in others. In drought years every mouthful became precious to a cow eating to store enough fat to trigger ovulation and to carry a growing fetus through a hard winter. Dominance would have a big payoff in those years. And dominance would payoff any time that the snow was deep. Foraging bison sweep the snow from the grass by swinging their heads from side to side and using their muzzles as plows. They clear little craters in the snow and eat the grass at the bottom. At least, they eat that grass unless and until a dominant makes them move on and takes over that patch. A dominant will eat everything it clears and some that it doesn't clear. A subordinate will eat only part of what it clears. That difference can be really big at crucial times. All other things being equal, the dominants will get fatter and the subordinates will get leaner. So the cows are interacting constantly, dominants and subordinates in a careful dance of distance; and being the dominant is worthwhile. A socioecologist can't resist asking what makes one of a pair dominant and the other subordinate. The answer turns out to depend on where you ask the question. Alan Rutberg asked it at the National Bison Range. These particular cows were, as my dad would have said, in grass up to their bellies. Every cow was well-nourished, and every year about 90 percent of the mature cows produced a calf. Alan worked out which cows were dominant in relation to which. He found that two-year-olds dominated one-year-olds, and three-year-olds dominated two-year-olds; through age eight, all older cows dominated all younger ones. When they were young, of course, the older cows were also bigger than the younger cows. But by the time they were three years old that was no longer so, for they'd reached their full size. Yet threeyear-olds, even when bigger, didn't dominate six-year-olds. It appeared that there were no upstarts because there was nothing to start them up. In the midst of abundant food, they had nothing to gain and they just laid low. Among adults there was no relationship between weight and dominance. What mattered was ecological resources, for which animals compete when necessary-and dominance status is the coin of compe-

25

RELATIONSHIPS

tition. It does seem odd that Alan saw two aggressive encounters per cow per hour if these cows weren't competing for scarce resources. Yet it's typical of a dominance system that the dominant individuals launch a steady stream of preemptive bullyings-sort of like those "Don't even think about it" admonitions. But buffalo cow society was very different on Catalina Island. Once severely overgrazed, Catalina, despite decades of restoration, offered slim pickings to the 400 head of bison grazing there; and that raised the stakes for the cows. At the same time that about 90 percent of mature cows on the National Bison Range gave birth each year, on Catalina only about 30 percent annually were giving birth. We captured seven cows in a corral, determined their weight and age, and then hung radio transmitters around their necks and watched them. In a corral the cows had a strict dominance hierarchy. That hierarchy correlated perfectly with body weight: every cow dominated every lighter cow and was subordinate to every heavier one. Weight was all that mattered-age was irrelevant. Dominant cows ate better than subordinate, going through the oat hay in the feed troughs to get the grain that fell from the shattered heads and leaving the straw for the less dominant who were waiting their turn. After a few days of watching, we turned the cows back to the Range and followed them for four years. They went their separate ways, and we only rarely saw them together again. The more dominant they were in that corral for those few days, the more calves they had. The heaviest, most dominant cows calved every year; the lightest, most subordinate not at all. That is a huge difference. Natural selection is nothing more than some individuals rearing more offspring than others. If eating better produces more offspring, then any trait that supports better eating will spread. And we know that at least sometimes dominant cows eat better than subordinates. So it seems that on Catalina, where dominance pays off, cows compete for it. And rather than order of birth determining the outcome, there is a perfect correlation between cows' weight and their dominance status. It looks as if scarce food raised the level of competition by making dominance worth taking more risks and spending more energy; either heavier cows became dominant or dominant cows became heavier.

26

COW TO COW

Bison cows are thus no Johnny one-notes. Their forebears must have experienced both plenty and scarcity in their evolutionary history-times when dominance was worth fighting for and times when it wasn't. Changing circumstances select for changeable behavior, with different strategies for different times and places. The bison pay the costs of striving for dominance when the benefits are high, and don't when the benefits are low.

27

CHAPTER 3

Cow to Calf

On the National Bison Range calves are born in April and May-spring fever season. The snow has melted and the earth is warming. The new grass growth's vibrant green is eclipsing the brown, dried grasses of winter. The golden yellow of arrowleaf balsam root and the purple of lupine contrast intensely with the new grass. I have watched dozens of calves emerge into this idyllic world. It's a setting to encourage relaxation, even lassitude--I feel it, but the calves don't seem to. Take the one I'm watching just now. Within a minute or two, as soon as his mother has freed him from the membrane that surrounded him in the womb, he begins a frantic-seeming struggle to get to his feet. He gets halfway up several times, and falls forward, backward, and sideways. I think, "Take it easy, little one, rest a minute.

There's no rush!" But the brain that has guided calves to adulthood for thousands of generations knows better. The calf hasn't got a minute to spare. Wolves may arrive any moment. A late winter storm could drop six inches of snow tonight, and winter is certain to return in a few months. Winter and wolves. These ancient forces selected which among calves past would bear or sire another generation. And so they have shaped this calf-bones, brains, and behavior. To survive them the calf must grow: bigger, faster, fatter. So much growing to do, in so little time. The calf responds to these imperatives as to whispers from the unbroken chain of ancestors who obeyed the commands and lived to pass them on: "The wolves will come. Stand and grow stronger. Exercise and grow fleeter." IJWinter is coming. Eat and grow longer legs before the snow is deep. Eat and grow a bigger body that will conserve heat in the winter's cold. Eat and store fat for energy when food is short and nights are long and cold." So the calf lives to grow and grows to live. It must stay alive to be able to grow, it must grow to be able to stay alive. That is its work at this stage

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COW TO CALF

of its life. We're tempted to think of the calf as an incompetent adult, especially when we see a male a few weeks old charging about butting heads with animals twenty times its size, or enthusiastically but fruitlessly mounting a female calf. But its work is not to be an imperfect adult (or any other kind of adult); it is to be a perfect calf. The same work any other developing creature has. Ruminants demonstrate the difference in the work to be done with rare clarity. Their family name comes from the practice of bringing up fistsized wads (boluses) of partially digested plants from the fore part of the stomach and ruminating: meditatively chewing, then reswallowing, the boluses. Adult bison spend a good part of their day ruminating; it's an essential part of their digestion. But bison calves don't ruminate for the first three months. Not because they are imperfect adults, but because they don't yet get their nutrition from plants. At that stage they are nonruminating ruminants, which is exactly what they need to be. Mother's milk makes this way of life possible, and the relationship between the cow and the calf is what makes mother's milk available. A buffalo's first breath, its first sight of light, comes as it emerges from a warm womb into the brightness of a spring day or the dimness of a spring night. It's not alone. Mom is there, a bit tired from her labor but ready to begin a foundational relationship-mother and child. The calf is still tan-

gled in the membranes that enclosed it in its mother's womb, and the tattered, bloody remains of the placenta and related membranes dangle from beneath the cow's tail. Mother is avid for her baby. She licks, pulls away, even eats the membrane that entangles it. When the membrane is gone she licks the drenched coat beneath it. Love at first sight comes only to those who are ready for it, and this mother is ready. As she gave birth, oxytocin, a hormone from her pituitary, surged into her bloodstream and onward to her brain as it does in every mammal, humans included. As her womb emptied, her heart filled and her senses absorbed the sight, sound, taste, and smell of what would be, for the months to come, her one and only. The one living thing she will nurture-and sometimes even challenge hungry wolves to protect.

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RELATIONSHIPS

The calf needs to stay close to its mother, and to nurse. Evolution not only made nursing a necessity but set up a positive feedback loop. Nursing releases oxytocin, so the more the calf nurses the more mother loves it; and the more she loves it the more she allows it to nurse. She even lets it interrupt her travel when it presses its body across her front legs, then dives for her udder when she pauses. A bison calf's first priority is to get to its feet and walk. By the stopwatch I kept time with as I watched a dozen births, that takes all of seven or eight minutes. An hour-old calf can scamper pretty well. It's a wonderful adaptation to being born in plain sight on a prairie with wolves about, but it makes the calf a challenge to keep in touch with-it's like a ball that never stops bouncing. The bouncing baby bison doesn't bounce aimlessly. It bounces toward something big and close. Mom is big and close and the ball usually bounces her way. But sometimes it fixes its eye on some other bison that passes by and rushes after it. Then mother chases both down and retrieves her young. A calf a few months old that loses its mother will attach itself to anything large and moving. An orphan calf followed Captain Meriwether Lewis all one afternoon as he walked west beside the Missouri

River. Most hoofed babies are like baby bison-on their feet and ready to move the day they're born. We say they're precocial. Some species stay with mother from birth on-we call that the follower strategy. In some species mothers hide their babies and leave them, returning only to nurse them. We call that the hider strategy. Pronghorn are a hider species. Pronghorn fawns are odorless, and small enough to disappear by lying down behind grass ten inches tall. With their coloring and curled-up posture they bear a striking resemblance to a large, dry buffalo chip when viewed from above. Mother returns to the area periodically, stops near the young-nearly always twins-and calls. The fawns jump up, rush to mother, and nurse. After several minutes of enthusiastic nursing the young walk off and lie down fifteen or twenty yards from the end of mother's scent trail. This way a coyote can't follow a mother's scent to her fawns.

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COW TO CALF

Follower versus hider is a very useful distinction, but more as a way to identify basic strategies than as a classificatory scheme into which the particular behavior of particular animals must be forced. In the latter case it tends to blur the middle ground. The research biologist Wendy Green has pointed out that yes, bison calves are followers, but unlike some young ungulates who stay at mother's heels, often they're following the herd as much as their mother. Being in the herd has one of the advantages of being with mother-it's safer than being alone. The herd's adults might challenge wolves. Even if they don't, there's a good chance some other calf will be between you and the wolves. That means you don't have to outrun the wolves, you just have to outrun that other calf. A big downside is that you may lose contact with mother if the herd stampedes. For bison, as for people, keeping in touch can be figurative as well as literal. Many animals that move in herds or flocks have a call that signals with much the same effect of a human crying out, "I'm here; where are you?" The bison version of this "contact call" moved my veterinarian grandfather, when he was superintendent of the National Bison Range, to refer to the bison as "my pigs." You hear their call occasionally while the animals are grazing, more frequently as a group of cows and calves walk along as they're going somewhere-say to water. You hear a lot of grunting when a herd has just stampeded, separating cows and calves. Mothers and calves grunt to each

other across a poststampede herd and track the right-sounding voice they hear to a reunion. The grunts that are so alike to our ears are different enough to theirs to convey identity-like a familiar voice saying hello when answering your phone call. But like someone responding to an onthe-phone hello, the hearer sometimes gets it wrong. I've several times seen a cow and a calf exchange grunts across a herd, make their way through it and come together, noses extended, only to fail the gold standard-the sniff test. Away they go, grunting again and listening again, for the grunt. This too shall pass, but not for several months; and while it lasts it is the most intense relationship of a bison's life. The intensity will subside with weaning, sometime after six months, but the relationship, particu-

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RELATIONSHIPS

larly if the calf is female, can last much longer-can, but doesn't always. To measure the life span of a relationship, you must record first its birth, then its death. It's easy to say when a cow-calf relationship begins, but harder to say when it is over. So we rely on proximity-inferring that the closer the bodies, the closer the relationship. But how close is close? I used a pretty crude measure to follow cow-calf relationships among the 400 head on Catalina Island. Cows and calves there are usually in small groups. My graduate students and I disregarded anything subtle going on within groups. We simply determined how old the calf was when it became so independent of its mother that it was no more likely to be in the same group with mom than it was to be in a group with any other individual. The bull calves we watched were no more likely to be with their mother's group than with any other group from six months on. The heifer calves were in the same groups for a year, then they too were independent. Yet the daughters that Wendy Green followed at Wind Cave National Park in South Dakota and those that the zoologists Jim Shaw and Tracy Carter followed at Wichita Mountains Wildlife Refuge in Oklahoma stayed with mom a year or even two years longer than those on Catalina. I'm not certain why daughters separated from mothers earlier on Catalina, but I have a hypothesis that supposes they're trading the benefits of staying with mom against the benefits of maximizing good nutrition. Staying close to mom is safer and less socially stressful. When some tenmonth-old orphan calves were put with a herd of strangers, they were harassed more than were same-aged calves whose mothers were presentmost of the harassment came from animals one year older. Yet staying close to mom also has a cost: spending time in places or groups where a growing bison finds it harder to get its fill of needed grass. The more mom's needs and capabilities differ from her daughter's, the greater the cost. Scarce food and far-apart water sources would exacerbate such a cost. Food was much scarcer on Catalina. The whole island had once been severely overgrazed by cattle and goats. The range was being cared for and was recovering, but forage was still scarce there. The adult bison were small and, as noted in chapter 2, only about 30 percent of the mature cows had a calf each year. At Wind Cave and the Wichita Mountains forage was

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COW TO CALF

much better, bison were bigger, and 75 percent or more of the cows calved each year. Daughter bison may be programmed to detach themselves under nutritional stress: they may be designed so that hunger and thirst are stronger forces than the attraction to mom. These are the costs and benefits a calf must weigh, and their difference in different areas may determine when daughters leave mothers. While daughters must choose when to end the relationship, mothers must choose where to begin it-where to give birth. She and the calf need some way to ensure that each develops a relationship with the right other individual-smells the right smell, hears the right voice. For though they have been intensely connected physiologically-sharing one body and one blood supply-socially they are complete strangers. They must create the relationship quickly and surely, before the precocious calf becomes so mobile that it mingles with others that look and sound very like it. Cows can make sure of that privacy by being alone when they give birth. On Catalina Island most cows gave birth in solitude, usually among bushes, scrub oak, ceanothus, or coast live oak trees. There they were hard to see. They had both privacy and shelter from prying eyes-they had cover. But on the National Bison Range most cows stayed in their herd to give birth. There were exceptions to both rules, but the general patterns showed a striking distinction between the two places. This difference must have a cause, and my reasoning centers around the trade-offs be-

tween privacy and predation. Wolves hunt mostly by sight. If wolves are your worry, then being out of their sight is best. If there are bushes or trees you can hide among them. But if the tallest plants are ankle-high grasses, the only thing big enough to hide behind is another bison-or better still, a bunch of bison. On the National Bison Range I was watching cows give birth on a grassland; on Catalina Island they were giving birth in a coastal scrub community. Wherever the relationship begins, it eventually ends. The relationship is strong for several months, but after only one week the calf's independence strengthens. It leaves the mother more often and stays away longer, usually in the company of several calves. We see the most detail about this stage of a calf's development in Wendy Green's data on thirteen cows and their daughters. As the daughters entered their third month, their be-

33

RELATIONSHIPS

havior changed sharply. They suckled less, rested less, and grazed more, usually with their mothers. Keeping in touch with mother is a matter of life and death for the calf, and keeping in touch with her calf-her stake in the next generation-is almost as important to mother. Gestation in bison is nine months, so the breeding season starts just as most calves enter their fourth month. Some of the mothers Wendy was following got pregnant and some (mostly older cows) didn't. Pregnancy set up a classic conflict of interests, called parent-offspring conflict-the result of a competition between the best interests of the current calf and those of the future calf. Selection has prepared a pregnant mother to prepare for another calf. Part of that preparation takes the form of ceasing to invest in her current calf so she can rebuild herself to deliver a healthy calf in just nine months. Thus the best deal for the cow is to invest less in this calf so she can invest more in the calf to come. She's equally related to both, and to her calves that may come even further in the future. That's not the best deal for the current calf. Mother's new calf is unlikely to be closer than a half sibling-sharing one-fourth of its genes. All things considered, its best deal is for mother to continue to invest in it no matter the cost to its future half siblings. The result is a classic conflict of genetic interest. Pregnancy is crunch time. Now the cow has one calf at her udder and one in her womb. Her resources-her energy and her body's tissues-are finite, and she must divide them between her two calves. Wendy's pregnant cows' behavior toward the one at their udder changed sharply, unlike the behavior of the mothers that didn't get pregnant. Through the next three months (until the calf was six months old), pregnant mothers were more than twice as aggressive toward their calves when they nursed and attempted to nurse. From six months on, the differences were even more dramatic. Pregnant mothers nursed only 10 percent as much as nonpregnant mothers, and spent more than ten times as much time grazing while the calf nursed. But the calf isn't just pushed away, it also walks away-choosing to spend more and more time with age-mates and getting more and more of its nutrition from the grasses it grazes. Sons become mere acquaintances first, but daughters eventually do too, when they have their first calf, if

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COW TO CALF

not before. Each is pursuing the path that will maximize the number of its genes in the next generation. They have moved on. The bond has served its purpose and dissolved. Daughters will experience its intensity again when they become mothers, but sons will never again experience a relationship anything like it.

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I

The Machinery

if a Bison's Life

I

i!

I I

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.....

An animal is a set of mechanisms-a collection of physical and chemical phenomena. Oxygen comes and carbon dioxide goes. Nerve impulses stream from the eyes and ears to the brain and from there to the muscles. The muscles contract or relax. There is so much to tell about mechanisms. Much too much to include here. But there is space to touch on a little of the physics and chemistry of bison life. I've chosen three aspects: movement, digestion, and body temperature maintenance.

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CHAPTER 4

Bison Athletics

Even though they're imaginary, we can't imagine Elsie the contented cow or Ferdinand the flower-loving bull winning a footrace with Silver, the Lone Ranger's horse-and they couldn't. But Harvey Wallbanger, a fleshand-blood buffalo, regularly showed his heels to racehorses in the 440yard dash. To be sure, these humiliated horses were not the fastest ever to go to the starting gate-in fact, many were among the slowest in America's racing stables. Still, they were racehorses, while Harvey was basically an off-the-rack buffalo: the one who happened to be handy when a shrewd cowboy decided to go into the buffalo-racing business. Harvey's triumph would not have surprised the Sioux, Crow, Blackfeet, Comanches, and Cheyennes who hunted buffalo from horseback for nearly two centuries. While most of their horses could overtake one buffalo/ only a few could overtake several buffalo in one chase. A buffalo's skinny rump and long front legs give it a long-enduring stride-a good

match for a coursing predator like the wolf. It is an animal faster than, well, some speeding racehorses, and able to leap tall road cuts at a single bound. Grazing buffalo show no signs of Harvey Wallbanger's athleticism. They plod in short steps from one mouthful of grass to the next. When they move to water it's at a faster but still patient and economical walk. They lie down and get up with deep sighs and a cautious folding and unfolding of their legs that suggests the outcome is in doubt. Yet they are capable, at any second, of a memorable athletic moment. I'm watching a mature bull standing alone on a dirt road on the National Bison Range. He's the only buffalo around, and I have set up my movie camera, so I'm watching him through the viewfinder-finger on the shutter button-wishing, as a man with a movie camera will, that the

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A BISON'S LIFE

subject would do something footage-worthy. He stands broadside to the road's line of travel, his front feet at the bottom of the cutbank where the road is in a trough cut through a low hill to ease the grade. His right horn slips into the cutbank and cuts a horizontal groove. He glances up to the top of the cutbank, six feet above the road, cuts another grove with his left horn, glances up again, then-without seeming to gather himself-leaps to the top of the cutbank, lands upright on all four feet, and calmly surveys his new view. My finger is still on the shutter button, and I still haven't pressed it. I've just seen 2,000 pounds of buffalo do a standing high jump of six feet. My breath is quick and a little shaky, but the bull is perfectly calm. After standing for a minute he plods off. No high fives, or twos for that matter, but his patient, confident amble seemed an understated celebration of its own-"Not bad for a big bull with a skinny butt, eh?" At a cattle guard, the road through a fence is open to vehicles but not to livestock. You make a cattle guard by cutting a hole in the fence as wide as the road, digging a shallow pit the width of the road and (usually) eight feet long. Then you cover the pit with parallel steel bars three or four inches wide, an inch or so thick, and as long as the road is wide. Set them on edge about six inches apart, perpendicular to the alignment of the road. Wheels easily roll across it, but cattle, faced with the choice of a long broad jump or a walk on a surface their feet might slip through, choose neither and so stay on one side of the fence. Management installed some cattle guards on the National Bison Range. They were working fine for buffalo cows and calves, but not very well for bulls. Bulls were getting past them somehow, and one day I saw how. A bull walked calmly up the road to a cattle guard, stood placidly on one side of it, then hopped-no other word would really describe it-across, landing on all four feet on the other side. This hop had to be long enough to deposit his hind feet on the far side of the cattle guard, so he cleared the width of the cattle guard plus the distance from his front feet to his rear feet, say another six feet, for a total of fourteen feet. A very impressive standing broad jump. Well, at least I was impressed. If the bull was impressed, it didn't show. He stood where he had landed for a quiet moment, then, with an air of "been here, done this," cropped a mouthful of grass from the side of the road and walked on-patiently and efficiently.

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BISON ATHLETICS

National Bison Range personnel countE'red the buffalo hop strategy by placing two cattle guards end to end. No,v a bull would have to hop sixteen plus six feet; and so far as I know, none ever did. But buffalo bulldom had not exhausted the arrows in its quiver. One day in breeding season I pulled my ancient Jeep to the side of the road, just after passing through one of these amplified cattle guards, and ~,at looking at the herd ahead of me. From behind came a distinct pinging, as though someone were tapping something metal with a piece of wood. A bull's image filled most of my rearview mirror. He was in the middip of the cattle guard, placing his feet delicately, cautiously, one at a time but still confidently, so they were centered on the narrow bars of the cattle guard as he walked across with all the poise, and a good bit of the daring, I)f a man on a tightrope. I would not have been any more astonished if he had also been singing "Tiptoe through the Tulips" in a friendly falsetto. When he reached solid ground he walked past me and joined the herd, lelving me to ponder the demonstration of footwork finesse I had just witnessed and somehow make it fit with the demonstrations of brute power I had also seen. For while buffalo leaps and sprints are spectacular, walking is the athletic talent that brings the animals to fooe and water day after day. Bison are roamers. Even in the confined spaces where they live today, they will travel ten or twelve miles overnight. On the Great Plains they may have traveled hundreds of miles from season tc) season-perhaps searching for a better place to spend the winter, or for c location with fewer human beings. They surely gained something from each step of those journeys, but (and here is where a physical feat is required) to be profitable each had to gain them enough to offset its costs. And the cost is high; bulls weigh about a ton. When a vehicle that size is fueled vrith blades of grass, every blade has to count. So the athletic challenge becomes like one of those competitions to see how far a vehicle can travel )n a gallon of gas. It's all about efficiency-getting the most out of ever/ drop of gas or blade of grass. Why is it that an animal that runs so fast walks so slow? It's all about energy. Buffalo, and just about everything else that walks, set a pace that matches the natural period of the pendulum constituted by its leg. A buffalo's leg, like yours and mine, swings forward and back as the anin1al

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A

BISON'S LIFE

walks, so it's a pendulum. The key point is that every pendulum has a most efficient swinging speed, the speed at which it uses the least energy to complete a cycle: that's its natural period. When you walk at your legs' natural period, a good bit of the energy that moves a foot forward at each step comes from your legs' pendulum swing; in this way, each time a foot swings forward it's recovering part of the energy invested in the previous step. At its natural period pace a buffalo, or any other four-footed beast, can recover 35 to 50 percent of the energy put into each stride. But when it comes to walking, two legs are better. Bipedal striders (creatures like ostriches and us) recover more, maybe as much as 70 percent, of each stride's energy just by walking naturally. How fast is that? A pendulum's natural period is determined by its length, but something a little tricky happens here. Suppose you found a bison whose hind legs happened to be the same length as yours and you walked beside it (at a safe distance), matching it stride for stride as it walked to water. Strange as it seems, you would not both be walking most efficiently. Your legs and his are the same length as legs, but not as pendulun1s-the "length" of a pendulum is determined by the distribution of its weight. The closer a pendulum's weight is to the place where it pivots, the shorter the pendulum and the shorter its natural period. A buffalo's legs are heavier at the top and skinnier at the bottom than yours, so its natural period is faster. You'd have to hurry your pace to keep up. How much you' cl hurry would depend partly on your choice of shoes that day. Featherweight footwear would make your leg a significantly shorter, faster pendulum than would a five-pound pair of waffle-soled, insulated mountain boots. Come to think of it, moccasins would be about the best choice you could make. But you can bet your best moccasins that Harvey Wallbanger didn't walk away from those racehorses. Both parties were galloping flat out for a quarter of a mile, and both could gallop-a little more slowly, to be sure-for miles and miles, as most hoofed animals can. How do they get the energy? By conserving it. This illustrates not the pendulum effect, since the bison's legs are moving much faster than their natural period, but more a pogo stick effect. As their feet land, they store the force of gravity in tendons and ligaments threaded the long way around the joints in

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BISON ATHLETICS

their legs. When their legs flex with gravity, those ligaments and tendons stretch like the spring on a screen door, and that energy is recovered as the leg straightens for the next step. Imagine a door spring attached at one end to the back of your knee, stretched down the back of your leg over your heel along the sole of your foot, and attached at its other end to the bottom of your toes. If you ran on your toes and flexed your ankle with every step the spring would store energy as you landed on your foot and return it as you strode ahead. That's one of several springs in a hoofed animal's leg and foot-sort of an elaborate pogo stick. (But it's also different from a pogo stick, which stores energy by compressing a coil spring; a tendon stores energy by stretching.) Sheep can recover about 30 percent of their running energy this way, and camels may recover 50 percent. Buffalo fall somewhere in that range. We humans don't have the feet for this feat. Bison are always on their toes: that joint about a third of the way up their leg isn't a backward knee but the heel of their foot, and the tendon from their real knee to their toes is long and stretchy.

THE QUICK AND THE DEAD

Bison athleticism isn't all track-and-field events and efficiency contests. They fight, too (at least the bulls do), and power alone won't win a fight

or even get a contender out of one alive. A bull has to twist and turnquickly enough to protect his own flanks, quickly enough to get a horn into his opponent's flank. Selection is intense. Bulls are wounded every breeding season, and in most years 5 or 6 percent of the mature bulls in any population die of their wounds. So the bulls are built to be quick in battle. To protect their body with their head, they need to pivot around their front feet. They have a great form for that function: much of their weight is centered over their front legs-their diminutive rear end is balanced in part by their massive head and neck. And the weight of their head is partly suspended from a point above their shoulders. There, rays of bone a foot long (called vertebral processes) project up from their vertebrae and anchor a tendon that attaches to the rear of the skull. This efficiently supports the transfer of their head's

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BISON'S LIFE

weight to their front feet, on which they pirouette on the sod like a hockey player on ice. When I started to study buffalo a colleague said, "But they're just humpbacked cows!" Both walk on four legs, eat grass, and ruminate, but cattle were selected in a competition to supply milk and meat to humans cheaply and safely. Bison were selected in a competition to produce more bison-a competition in which the better athlete wins. That competition honed their shape and substance from small haunches to high hump, from size and strength to agility, from speed to stamina. People sometimes say the competition in which bulls won breeding rights selected the "best" bulls, suggesting they do everything well. In fact, their specialization has cost them. One day I watched three mature bulls and a young one chase a cow. For the first 200 yards the older bulls ran easily, their long hair flowing in the wind. They even tried to mount the cow at a full gallop. But when the cow and the young bull circled back, still at a full gallop after a long run, the mature bulls followed at a wobbly walk, tongues hanging out and sides heaving. They were just too big to keep up the pace the smaller animals set. Natural selection has compromised much else to focus the bulls on one goal-forcing other bulls aside at tending time. It is then-when the bull moves to his task, beard swaying and pantaloons bouncing, belly lifted in an arch as he bellows a challenge-that he is perfect. And he is magnificent.

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CHAPTER 5

Digestion

Grass to Gas and Chips

When Buffalo Bill Cody took the Czarevitch on safari in what would become South Dakota, they rode through a sea of flesh at ground level, with more below ground and even some in the air. In just about every square mile, thousands of vertebrate hearts were beating every moment, sending hundreds of gallons of blood· coursing through thousands of miles of blood vessels. All this fabulous, teeming mass of animal matter and its motion was built from, and powered by, a growing grassland. A grassland's plants combine the energy from the sun with water and nutrients from the soil to grow and reproduce. These plants produce the stuff of life and growth for grass eaters. There are carbohydrates for energy and protein for growth and repairing body parts. Many a backyard lawn produces enough calories and nutrients, strictly speaking, to nourish its owner. But the process is not that simple, because plants fight back. Plants have their own uses for the energy they capture from the sun, just as animals that are the prey of others have their own uses for the energy they capture from the plants. And like prey animals, plants have evolved ways to defend themselves. They can't run and they can't hide, but they can be unpalatable, difficult to chew, or indigestible. They can even be lethally toxic. Plants put a good bit of energy into their defenses. For example, many plants produce tannin, which does nothing for the plant but makes it difficult for the animal that eats it to digest proteins. Many plant eaters, including humans, have evolved a countermeasureour saliva contains a molecule that binds with tannin and neutralizes it. The astringent taste of the neutralized tannin gives a sip of red wine its special flavor. And so coevolution goes-measure, countermeasure, counter-countermeasure. It's a sort of biological arms race made inevitable by the fact

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A BISON'S LIFE

of natural selection, and it has produced some elegant measures and countermeasures. Grass hasn't evolved tannin, but it stores most of its carbohydrates as cellulose, and until the cellulose has been digested the carbohydrates are not available. In turn, most of the Great Plains' big animals-bison, antelope, deer, and elk-counter cellulose with rumination, which turns grass into gas: figurative gas, as fuel to run their physical systems, and literal gas, as methane. Digesting anything is a strictly chemical matter of subjecting it to an enzyme that breaks certain molecular bonds, simple enough if you have the right enzyme. Put the food in your digestive tract, secrete the enzyme. Neither you nor I can secrete an enzyme that can digest cellulose. As a matter of fact, bison don't secrete such an enzyme either, but they rely on a method as good and in some ways better: they enlist colonies of bacteria.

ENZYME, ENZYME, WHO'S GOT THE ENZYME?

Reliance on bacteria is a wonderful strategy. Think of a thing, almost anything, that is or once was alive, and chances are good that some bacteria can digest it. That is to say, bacteria exist that have evolved an enzyme that can break the molecular bonds in such a way as to make the energy and nutrients available to those bacteria. Bison didn't evolve an enzyme that can digest cellulose, but they did evolve a happy home for bacteria that have evolved such an enzyme. The front part of their stomach is segmented off by a fold (the rumen) in which newly swallowed food is kept for a while. The fold probably came before grass appeared on the earth. It created a special place where food, as soon as it was swallowed, could be detoxified-the plant's chemical defenses neutralized-by some toxin-eating bacteria living there. But now it serves as a place where some very helpful bacteria put their enzymes to work digesting the cellulose. The ruminants have enlisted a powerful ally in their arms race with grass. A key to success in any arms race is how quickly measures can be developed to counter an opponent's previous development. The advantage therefore goes to the party that can evolve faster. Ruminants don't evolve faster than grasses, but bacteria, with dozens of generations in a

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RANCH HERD

This herd was photographed on Vermejo Ranch in northeastern New Mexico. Bison are better suited to western grasslands than are cattle, requiring less care and doing less damage. More than 95 percent of bison in North America are privately owned and live on ranches. There selective breeding will produce a domesticated form of bison with little wildness left.

SADDLED STEER ON CATALlNA ISLAND

Some buffalo, usually castrated males, have been trained to carry a rider or pull a cart. They remain dangerous.

HORSES

Reintroduced to North America by the Spanish after a 1O,ooo-year absence, horses transformed the buffalo's world. They multiplied the take by Native American hunters, supported European hunting, and competed for grass against both managed and wild herds.

WILD BULL RESISTING ROUNDUP

The bull pictured is reacting to men trying to move him through a corral on the National Bison Range during the annual roundup. Handling wild bison is difficult, dangerous, and expensive. Domestication will select for more tractable-hence less wildanimals. This bull's behavior will be tolerated in this publicly owned herd, but a rancher would be compelled to shoot him.

PLUGGED PRAIRIE DOG BURROW

The burrows of black-tailed prairie dogs have one high entrance and one at ground level; the differential creates Wind-powered ventilation. When rattlesnakes enter the burrow the prairie dogs sometimes use soil from the mound to plug the opening, as Debra Shier saw a male do here weeks ago. He then plugged a nearby ground-level opening. The prairie dogs usually reopen the burrow after a day or two, which allows the snake to escape.

SURVIVORS

A litter of young prairie dogs has reached midsummer without succumbing to predators or infanticidal relatives.

WHITE BUFFALO

A very rare white buffalo calf, born on the National Bison Range in 1937, is pictured with my grandfather. Then superintendent of the National Bison Range, he had bred an almost completely white bull back to that bull's mother. This was their offspring. Granddad appears to be smoking a celebratory cigar. White coats would absorb less of the sun's energy in winter, making cold weather more costly for white buffalo than for dark ones. (Photo credit: my mother, Joyce Norton Lott. )

PRONGHORN MALE IN MIDSUMMER

Although pronghorn have true horns (not antlers), the horn sheath is shed every fall, revealing a small bony core around which a new sheath forms in the spring. A scent gland lies under the dark cheek patch.

PRONGHORN MALE MARKING

A territorial male wets the top of a tall plant in his mouth, then coats it with a secretion from his cheek patch gland.

PRONGHORN DOES AND FAWNS

Female pronghorn and their fawns move about in small groups, spending most of their time in the parts of the grassland with the greatest number of broadleafed annual plants. When and where pronghorn are territorial, master bucks set up territories that include these preferred microhabitats.

BUFFALO BIRDS

These birds, now usually called "cowbirds," feed on the insects that flee the mouths and hooves of grazing buffalo. Since bison are nomadic, a buffalo bird's food supply may move several miles from one day to the next. Buffalo birds are parasitic brooders, laying their eggs in other birds' nests. Thus they too are free to roam.

DRINKING ON THE NATIONAL BISON RANGE

Bison cool their bodies by evaporating water from their lungs. On hot summer days they need a lot of water. On Catalina Island, cows go to water twice a day, drinking four to six gallons at a time. Bulls there drink once a day in the summer. I was unable to measure the amount consumed by the average bull.

WALLOWING

All bison wallow several times a day in summer, filling their hair with dust. The dust probably discourages insects and may reduce the bison's body temperature.

GROOMING

Bison groom their hair regularly, primarily with their tongue, but they use their horns and hooves on spots their tongue can't reach.

MOTHER AND CALF

The relationship between mother and calf is by far the strongest and longest in a buffalo's life. Bull calves stay with their mothers until they are weaned at about six months old. In some habitats, heifer calves stay with their mothers until they become mothers themselves.

WEEKS-OLD CALF NURSING

Bison calves are precocial-on their feet and able to walk and nurse less than ten minutes after being born. The pulse of oxytocin that facilitates birth for the cow also facilitates the mother's bonding with her calf.

SNOW CRATER

A cow feeding on grass at the bottom of a crater that she has cleared in the snow. A dominant cow could displace her and get the food benefit without any cost (paid in the effort to clear the snow).

WINTER FORAGING

These cows and calves are feeding in deep snow in Yellowstone Park. Bison reach the snow-covered grass by sweeping the snow away with their muzzles.

COPULATION

Penetration: at this point cows often begin to walk or run, but some stand-as this one did.

EJACULATION

The bull's hind feet are lifted clear of the ground by the contraction of his abdominal muscles.

COW MOUNTING BULL

Tending bulls sometimes become so preoccupied with their rivals that they don't detect the cow's readiness to breed. A neglected cow may mount the bull. This usually gives him the idea.

RUNNING COW

Shortly before they become receptive, most cows break away from the tending bull and run through the herd a few times. These runs attract the attention and pursuit of other bulls, thus inciting competition for tending rights.

TENDING

During the midsummer breeding season, individual bulls accompany particular cows-usually cows that will soon breed. In a given day all the bulls in a herd compete to tend the cows most likely to breed that day.

LIP-CURL

The lip-curl is technically called flehmen. Bulls thrust their muzzle into a cow's urine, then lip-curl. The bull's tongue flutters up and down rapidly, probably transporting the urine to his vomernasal organ in the roof of his mouth. Sensitive to the metabolic products of a cow's reproductive hormonal cycles, that organ enables the bull to predict when she will become receptive.

DISPLAY HAIR

Left Tip, named for his left horn's flattened tip, was photographed on July 22, 1972, with his head hair, beard, and front leg pantaloons intact.

DISPLAY HAIR LOSS

Left Tip was photographed on October 3, 1972. Most of the hair between his horns had been sheared off in fights, but his beard and pantaloons were still full at the end of the breeding and fighting season. They then molted.

LOCK OF HEAD HAIR

This lock of hair was sheared off in a fight. The shearing action of the horns has given the upper edge a straight line.

HEAD HAIR SHEARED BY FIGHTING

When bulls fight, the hair on their foreheads and between their horns is often caught between the horns, sheared off as the horns slide past each other, and tossed into the air. Such a lock of hair is in the air above these bulls.

GORED BULL

This bull was gored about ten days before being photographed, and the wound has become infected. Such infected wounds often kill bulls, but this bull recovered and was healthy two months later. A third of mature bulls have at least one rib that has been broken and has healed.

FLANK ATTACK

Most contact is head to head, but the bulls also circle or push past the opponent's defense and try to gore an exposed flank.

FIGHTING

In a herd with a natural sex ratio, about 5 to 10 percent of challenges lead to fights. In a breeding herd there can be dozens of fights on some days. The other herd members become habituated to the drama.

HEAD-TO-HEAD CLASH

Most fights are head-to-head clashes followed by head-to-head pushing. To point their horns forward, bison bulls must drop their heads very low.

NOD THREAT

The bulls approach closely with their heads to the side and intermittently swing their heads up and down in matched movements. If there is an attack, it comes during the head-low phase of the cycle.

HEAD-ON THREAT AND SUBMISSION

Two bulls were approaching each other after wallowing, when the bull on the right yielded by turning his head to the side.

THREAT WALLOWING

Challenging bison often wallow between bouts of bellows. Sometimes they use an established wallow; sometimes they tear up sod with their horns to make a new one. In either case, they often urinate into the wallow before rolling in it.

POST-THREAT WALLOWING

After wallowing less than half a minute, the challenging bulls rise to confront each other again.

BROADSIDE THREAT

The bull on the left threatens by standing stiffly broadside. He is also bellowing, with the tip of his tongue touching the roof of his mouth. The bull on the right turning his head away is signaling submission.

BREEDING HERD

This breeding-season herd is on the National Bison Range in western Montana. The mature bulls join the cow groups from mid-July to mid-August and compete to tend estrous cows.

COW PORTRAIT

BULL PORTRAIT

This cow has some soil caught in her eyelashes. Freezing water cannot accumulate in the extremely short hair surrounding her eyes. Domestic cattle are sometimes blinded by ice accumulating in the longer hair that surrounds their eyes.

The thick cushion of head hair may make a mature bull seem larger to competitors. It certainly absorbs some of the shock of battle. The base of a cow's horn is about the size of her eye. The base of a bull's horn, even in a young bull, is much larger than his eye.

DIGESTION

day, evolve faster than just about anything else. By enlisting bacteria in their cause, ruminants shifted from being slow to being blindingly fast in the evolution of countermeasures. The rumen becomes an arena in which different kinds of bacteria compete, enzyme against enzyme; the producer of the most efficient enzyme succeeds in expanding its population at the cost of the populations of its competitors. Bacterial digestion of plant materials is a common process with a common name-fermentation. And although bacteria are simple as life forms go, their chemistry is complex, and fermentation produces a complex outcome. They not only change cellulose to usable carbohydrates but also produce volatile fatty acids. Both are concentrated energy in a form bison can use. They are the gas from grass that makes the animal's heart beat and its feet move. Like aUliving things, these fermentation bacteria have waste products, which include alcohol. It's a sobering fact that 12 or 13 percent of a bottle of Dom Perignon Champagne is bacteria pee. For the bison a percentage of bacteria waste products that high would be a calamity, because it would mean that the bacteria were themselves using the energy their enzymes were releasing. Here we come to one of those built-in conflicts of interest that are part of nearly all relationships. Up to the point of converting cellulose to usable carbos and fatty acids, bison and bacteria have the same goals and collaborate. But now each has its own uses for the energy the enzymes have released-now they compete. It has to be a restrained competition, because both would starve if either were to get all the energy. Yet within the rumen, subtly different lines of bacteria must be striving to win a bigger share of the goodies. The bacteria-on-bacteria competition takes place in a friendly environmentthe bison's rumen-so the bison, being the environment as well as collaborator and competitor, has leverage that makes up for its slower evolutionary rate. When I was a soldier nearly fifty years ago, the cooks had a motto, "Just feed 'em-don't fatten 'em," which they enforced by rejecting requests for seconds. Bison don't limit their bacteria's food, but they severely limit their oxygen and their time. Some bacteria-anaerobic bacteria-ean function without oxygen, but they function slowly. In time they would use up the energy they have released from the grass, so bison don't give them

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time. They move the grass on out of the rumen after two or three days, pushing the partially digested food, and some of the bacteria that digested it to that point, further on. In the stomach, their own enzymes finish the job on the plants and digest some of the helpful bacteria as well. Timing is everything in this matter, and the ruminants have the timing down so well that they get about 90 percent of the energy for themselves. The mechanics of rumination are a bit inelegant. The ruminant assists the process by chewing its food after swallowing it-the bison brings up fist-sized wads of partially digested grass (cuds) from its rumen and chews them while lying at rest. If Buffalo Bill and the Czarevitch had sat in their saddles and contemplated a resting bison they'd have seen this; bison spend hours every day doing it. Although cud chewing-ruminating-gives them a faraway-focused, meditative, serene sort of look, it isn't an elegant activity. But as an adaptation, rumination is elegance itself. It is an adaptation that uses the process of adaptation-a sort of meta-adaptation, if there is such a thing-and it is beautiful to contemplate. It's so sophisticated that neither bison nor biologists would be likely to think of it, yet it was achieved by the perfectly purposeless, aimless, and automatic process of natural selection.

BUFFALO CHIPS

The immediate products of bison digestion are heat, energy, and tissue maintenance for the digesters' bodies. The final end products of bison digestion are buffalo calves and buffalo chips-a good many more chips than calves. People living on the plains burned buffalo chips as a cooking fuel. When they thought of chips, they thought of heat. When we in the computer age think of chips we think of information. A biologist who really knows his or her ... well, chips can extract an enormous amount of information from one. To appreciate a buffalo chip, you must ignore its rather unfortunate looks and any lingering odor, and think instead of where it's been. It has gone entirely through the animal from front to back, and by a very circuitous route. And every inch of the way, it has picked up traces of what is happening around it, while retaining its own identity. Think of it this

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way: if a computer memory chip traveled a similar electronic route, and had bits of data added to it at every step, it would emerge loaded with information. We couldn't wait to install it and read it. Small wonder, then, that biologists constantly upgrade their capacity to read those memory chips that digestion produces. Some years ago we figured out how to read in them a record of what the bison has eaten and what parasites live in its intestines. Analyzing parasites is the most straightforward part of this studyjust look and count. Figuring out what bison are eating is also straightforward, though rather more time-consuming. The cell walls of plants are pretty distinctive and pretty tough. You pick through the chips and locate cell walls. You compare the cell walls to the cell walls of plants from your reference collection-representatives of each plant that grows where the bison are feeding. The reference collection is needed to set some boundaries on your search for matches. And that's it. You can find out how many of the plants in its habitat a bison feeds on and, by comparing the percentage appearing in the chips with the percentage in the field, estimate which plants the bison favors. Recently we've learned to track hormones from their residues in feces. Tracking hormones is easier than determining diet, but a little more hightech. Progesterone shows up in feces. With a bit of biochemical abracadabra called enzymeimmunoassay you can discover how much a given (or taken) fecal sample contains. After you spend some more time, money, and enzymeimmunoassays calibrating the chips from bison feeding in a particular place, you can tell from her feces if a cow is in estrus. In their passage chips also pick up bison cells that contain the individual's complete genome. It is possible that they could reveal not only the individual's identity but perhaps the identity of its parents as well. So science will just keep chipping away at the secrets in the belly of the beast. What we can determine now is probably just the beginning. Everything that happens inside an animal produces a by-product that will reveal something about that process, and nearly all those by-products (and products) find their way into the lower end of the digestive tract and into the chips assembled there from the materials that have made the passage. There's probably at least one other way to get each bit of that informa-

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tion, but few other ways are as humane and efficient as chip analysis. No need to subdue the buffalo with a tranquilizing dart-and no worries that the hormone levels in the blood sample reflect short-term peaks or bottoms caused by the trauma of the sampling. Little wonder, then, that when the chips are down, the biologist's spirits are up. The investigator that at first seems a figure of fun, a dedicated pooper-scooper, is really the very model of a modern-day mammalogist.

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CHAPTER 6

Temperature Control

Big Medicine was the first white buffalo born in the twentieth century. His mother lived on the National Bison Range, where she gave birth to him in May 1933. My mother lived on the National Bison Range too, and she gave birth to me in December 1933. My maternal grandfather was the Bison Range superintendent then, and my dad worked for him. I won't say Granddad liked Big Medicine better than me, but the family photo collection contains many more snaps of Granddad and Big Medicine than of Granddad and me. Ah, well, a lot of us are born into somebody's shadow, and while I never outgrew Big Medicine's I have outlasted it by several decades. My family members weren't the only photographers besotted with Big Medicine-he was surely the most photographed buffalo that ever lived. Big Medicine was not a true albino. His eyes were pigmented and he had dark hair between his horns. But the rest of his hair was white. I've had a lot of years to think about Big Medicine, and a frequent thought is this: Why aren't all buffalo white? White is a good summer color. It reflects the sun's heat, and that heat is a fact of life for bison. They evolved in the grasslands, where summer sunshine is plentiful and shade is nonexistent; bison spend most of the long summer days absorbing the sun's heat into their dark coats. White is also a good winter color. Some rabbits turn white in the winter to blend with the snow, and so do some of the weasels that stalk them. Wolves hunt bison all winter long. Wouldn't blending with the background be a good idea? Rocky Mountain goats and DaB sheep-wolf prey on both-live around snow and wear white coats year round. But not only are white buffalo rare, they don't seem to do well. Far from going forth and multiplying, they dwindle and disappear. Granddad tried

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to promote them. With the directness of the stockman and veterinarian that he was, he arranged for Big Medicine to breed his mother as soon as he was old enough. They had a son who was a true albino. The nation's capital called and he was sent to the National Zoo in Washington, D.e. There he either ripped his leg in a fence and died of the resulting infection, as a zookeeper described to my brother, or swallowed some baling wire along with the baled hay he was being fed, as another story has it, and died too young to reproduce-zoo personnel have told both tales. Granddad intended to try for more, but the bureaucrats above himwisely, I think-decreed that the United States Fish and Wildlife Service was not in the business of producing freaks of nature. But nature has produced some in Alaska. When the state wanted to start several herds there, it got its stock from the National Bison Range. Big Medicine's gene was revealed in the coats of several calves born in Alaska, but none of them lived long enough to breed. Their early deaths may tell us something important about why white buffalo are so rare. The answer probably lies in winter. Someone once said, "Powerful though the sun's abundance is, its scarcity is even more powerful." Bison seldom if ever die of heat, but they often die of cold. The dark coat that makes the sun a nuisance in summer may be a lifesaver in winter. Bison evolved in really terrible winters; and even now, especially severe winters kill many of the old and the young. The sun is low and the days are short, but every calorie of heat absorbed from the sun is a calorie the bison does not have to manufacture from the scarce forage-forage that must be won by sweeping the snow from each bite with that heavy head-or drawn from its precious cache of calories in the form of stored fat. Like deer and elk, bison cut their energy output by losing their appetite. They eat less and produce less heat-and not just because food is scarcer in winter. Even when they can have all they want from full feeding troughs in an experimenter's corral, they eat 30 percent less food and produce 30 percent less heat in February and March than in April and May. The aphagia cuts down on low-profit energy expended in searching for food in a season when it would be scarce, but to accumulate the sun's energy they still must depend heavily on that dark hair.

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But there's more to hair than color; it also offers insulation. A high-tech way to census large, warm-blooded animals in winter is to fly with an infrared device-one that "sees" temperature. Wes Olson is the chief ranger at Elk Island Park in Alberta. He added an infrared detector to his elk, moose, and bison winter census a few years ago. The first flight was illuminating. There was a thick layer of fresh snow and the elk and moose stood out clearly against it, but hardly any bison showed up. There were a lot of warm crescents that made no sense. The eyes revealed what the infrared scope could not-the crescents were the bellies of reclining bison, the only part of them not covered by a thick layer of still-unmelted snow. The skin-side layer of the bison's coat was at body temperature, while the outside layer-only millimeters away-was below freezing. A buffalo robe was a possession prized by humans dwelling on the North American plains. It can keep you warm in a terrible storm. Cattle have replaced the buffalo, but there isn't much point in bundling up in a cattle robe. The buffalo robe's superiority is quite straightforward-a square inch of buffalo skin has ten times as many hairs growing from it as a square inch of cow skin. The difference, when temperatures and fat stores are low, is the difference between life and death. But when summer arrives there is a price to pay. The North American plains are a place of extreme heat as well as extreme cold. It's a bit like jumping from the deep freeze to the frying pan, and the challenge in summer is keeping cool. The first thing the bison do is shed their winter coats. The long, twisted, almost woolly hair of winter molts, and from the front shoulder back a sleek coat of short hair is revealed. It insulates only a little, allowing the nearly ceaseless wind of North America's grassland to blow away body heat. That surely helps; but still, the sun is hot, their dark hair absorbs its heat, and they also produce heat as they ferment their food and move around. If they couldn't get rid of the heat they generate and the heat they accumulate, they would soon be walking pot roasts. Lots of animals get rid of heat by evaporating water. Humans sweat, and when the sweat evaporates from our skin the process consumes heat, which is taken from our skin. The process has created a niche-our armpits-for the deodorant industry. Bison don't sweat, but they breathe,

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and lots of animals, again including humans, lose heat by evaporating water in their lungs. It was midsummer when Doug Propst first laid eyes on the Catalina Island bison herd he had been hired to manage. Doug was a Colorado cattleman, born, bred, and college-educated there. He told me that when he saw the first group of bison lying in the summer sun he was appalled. Their respiration rate (about forty breaths per minute) was consistent with only one thing. The whole herd had pneumonia! Imagine his relief on discovering that they were only keeping their cool. Evaporative cooling works well, but it has one major cost. You have to go through a lot of water in order that a lot of water can go through you. That internal supply must be replenished regularly. Surely the bison can do something to reduce the number of trips to water. Of course they could find some shade, but they don't seem much inclined to. It's astonishingly common to see them lying in the hot sun only twenty feet from dense shade. Perhaps their roots in the grassland where they evolved are most exposed here. There were no trees and no shade where they came from, so any inclination to search for it would have been a disadvantage. But grasslands at least have soil, and here we may be onto something. Bison wallow in the summer, especially during the middle of the day. Wallowing puts soil into and onto their coat. They can work so much nice, dry, powdery soil into their coat that as they walk away from the wallow it cascades down, jarred loose by each step. Like most old-timey bison watchers, I have always thought they were wallowing to make their hair a lousy place for lice and other parasites. I still think that's likely, but wallowing may also lower their heat load. Elephants have a heat problem much like bison have, and we know that a good coat of dirt is one of their solutions. We don't know that about bison-yet, but the odds are good that it also works for them.

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Whence The)' Came Forth) and How Much They Multiplied

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Every species has a history, and that history is a part of the species as much as an individual's history is a part of the individual. It both creates and limits the species' possibilities. Chapter 7, on ancestors and relatives, traces the bison lineage, especially in North America, and establishes the place of the modern species Bison bison, which emerged only about 5,000 years ago. Bison bison became one of the most abundant large land animals ofall time. Chapter 8 addresses the question of hOLD abundant it was before the European invasion of North America.

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CHAPTER 7

Ancestors and Relatives

ANCESTORS

Perhaps he fled the lions, his flying hooves hammering the grassy turf as he dashed past a herd of woolly mammoths or scattered a herd of Saiga antelope. Perhaps, being a prime bull at eight or nine years old, he faced and fought them. We don't know the details, but we do know the lions prevailed: in a matter of minutes there was one less buffalo alive in Alaska. His killers were American lions, similar enough to those in Africa today thatthough they were a bit bigger-the casual observer probably wouldn't distinguish them. Very likely they hunted and killed in the same way. We know the essentials about this violent death-who was killed, who killed him, and how and when and why (the lions were hungry) he was killed. There was a witness, the dead bull himself, and though he was silenced 36,000 years ago, he has testified through the forensic skills of the paleontologist Dale Guthrie. He is not one of the anonymous dead; he has a name: Blue Babe. He is here to tell his story because after the lions killed him and made a meal of his hump, a mud slide buried him. The mud froze, and the mud and Blue Babe remained frozen until a gold miner washed away the mud and revealed the mummy one July day in 1979. Copper precipitation had given Blue Babe's hide a blue tint and his hump had gone to fill the lions' stomachs, but the rest of him was remarkably well preserved. The tooth and claw marks in his hide were still so clear that Dale could take an American lion's skull, place its canine teeth on the marks left by the killer's canines, and see a perfect match. Even the flesh was so well preserved that when the corpse had yielded all its secrets Dale and his colleagues made an acceptable stew with a bit of the meat. Blue Babe had died in good condition, probably in early winter.

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WHENCE THEY CAME FORTH

Blue Babe was a Bison priscus-at least two phylogenetic steps back from today's Bison bison. He was very like his ancestors that came to North America from Siberia. It wasn't a long journey. When the route was dry, bison could have walked from Siberia to Alaska in three or four days. During ice ages glaciers accumulate so much of the earth's water on the continents that the sea level falls below the northern part of the Bering Sea's bottom, which is then called "Beringia." When Beringia connects Siberia and Alaska above sea level, it is often called the "Bering Land Bridge." Calling it a bridge makes it sound narrow, but it's really a subcontinent, at times 600 miles wide-leaving plenty of room for gradual colonization and species dispersal in both directions. The first bison to cross Beringia were not the first bison. Bison branched off from the primitive cow family line-Leptobos-about a million years ago. The first bison were small-bodied, small-horned, fast-moving residents of forest edges and meadows. Gradually the bison line became northern specialists, able to live where other cattle couldn't. They also became open grassland specialists. The Siberian steppe was a northern grassland, and bison became important members of that community. Bison taxonomists call this bison B. priscus. It was B. priscus that grazed its way from Siberia across Beringia to Alaska, perhaps as early as 600,000 years ago, perhaps as recently as 300,000 years ago. By then they had bigger bodies and bigger horns, and weren't quite as fleet of foot. B. priscus stayed north, a Widespread and abundant grazer on the iceage region that Dale has called the "Mammoth Steppe." It includes not just Beringia but also eastern Siberia and northwestern Alaska. Winters there were cold, but grasses grew abundantly in the long days of summer and supported a large grazing community. The three most important grazers were woolly mammoths, horses, and bison. Mammoths and horses became a bit smaller in this environment. But bison, the only ruminant of the three, apparently took advantage of a ruminant's potential for rapid growth and became larger. There is some disagreement about exactly what happened next. Bison fossils were first studied and classified at a time when taxonomists thought all members of a species were very similar to all others of the same age and sex class. Therefore, they saw modest differences between

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sets of bison skulls as signifying separate genetic lines and divided the bison on the Mammoth Steppe into several species. Some taxonomists still prefer that scenario. But we now know that many species are plastic. Their bodies and bones can differ in different places or at different times but still be from one species, able to produce healthy offspring from the mating of individuals of quite different sizes and shapes. Think of dogs. If we look at B. priscus with dogs in mind, the modest differences in skull shapes and sizes from place to place and from time to time fit easily into a picture of one plastic species persisting over several hundred thousand years. I side with those who favor this scenario. B. priscus did produce some offshoots that were clearly different species. One was a giant that developed from a line that reached central North America. B. latifrons stood some 20 percent taller than modern bison and the bony cores of its horns spanned six feet. With the sheaths in place, the horns must have been nearly seven feet on the living animal; and B. latifrons must have weighed at least a third more than modern bison, putting bulls close to 3,000 pounds. B. latifrons may have appeared as early as 300,000 years ago. These bison lived all over the region that has become the United States, but they were most abundant in the West, along the eastern edge of the Rocky Mountains, in the Great Basin Area-Nevada, Utah, southern Idaho, and Arizona-and in California. A few years ago construction excavation unearthed a B. latifrons in downtown San Francisco. It had lived there 25,000 years ago, when San Francisco Bay was a wooded grassland valley with a river running through it. The pace of bison evolution stepped up sharply about this time. The San Francisco B. latifrons was near the end of that line; no fossils younger than 22,000 years have been found. But B. latifrons probably gave rise to its successor-B. antiquus. B. antiquus lived in the same general regions, but was smaller bodied and much smaller horned. Its life as a species was short: it was born as B. latifrons died and then disappeared about 12,000 years later. B. antiquus was replaced in much of its range by B. occidentalis, a smaller bison probably born of the B. priscus line still occupying the Mammoth Steppe. B. occidentalis was smaller and smaller horned than B. priscus; and unlike any bison before it, its horns pointed up, parallel to the plane of its

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face from nose to forehead, instead of pointing forward through that plane. For a short time B. antiquus and B. occidentalis shared the Great Plains, but B. antiquus soon faded away. B. occidentalis never expanded into all B. antiquus's habitat-it never appeared in California, for example-but B. antiquus died out everywhere by about 10,000 years ago. B. occidentalis had an even shorter life as a species. It prospered, not only filling most of the space B. antiquus left vacant but becoming much more numerous even as the other members of the grassland communityhorses, camels, woolly mammoths, musk oxen-faded rapidly. Yet in only about 5,000 years it was replaced by today's still smaller descendant: B. bison. B. bison is the smallest bison that ever lived in North America and became by far the most abundant. Bison changed little for at least a quarter of a million years, then changed a great deal during the last 10,000 to 12,000 years-B. antiquus died out; B. occidentalis appeared and then died out as B. bison appeared. Even more dramatic changes have recently overtaken other large North American mammals in the same period. While bison were reinventing themselves, the Pleistocene extinction, a radical downsizing of the number of large mammal species, swept North America. Horses, camels, mammoths, mastodons-after millions of years of evolution in North America-all vanished around 10,000 to 12,000 years ago. Their exit was followed, or accompanied, by that of a suite of large predators-the giant short-faced bear, the American lion, the dire wolf, several species of sabertoothed cats. Many bird species vanished at the same time. There are several explanations for this great species loss. One theory argues that the trigger, in fact the fatal bullet, was the arrival of another large mammalian predator-humans. It's not certain just what manner of humans first came to North America or when they arrived. But it seems clear that North America was peopled by 12,000 years ago, and that those people hunted large mammals. There is a school of thought, led by the archaeologist Paul Martin, that lays the Pleistocene extinction at the moccasin-clad feet of these early hunters. In this Pleistocene overkill theory, Martin envisions a narrow band of human hunters extending from coast to coast and descending from north to south, killing virtually all members of most large prey species as they moved.

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Most ecologists doubt that's the whole story. North America is a big continent, and it was inhabited by tens or perhaps hundreds of millions of large animals that were being born as well as dying. To drive even one abundant species to extinction would be a formidable task. To drive several large grassland species to extinction simultaneously would be a prodigious feat. That's one of the reasons many ecologists are skeptical about the Pleistocene overkill hypothesis. Another reason is that there were other powerful forces at work. Climate and habitat changed rapidly and dramatically as the last ice age ended 10,000 to 12,000 years ago. California, for example, no longer had summer rainfall. The grasses dependent on that rainfall died out, and buffalo, which need grasses that grow in the summer, dwindled away. The grasslands east of the Rocky Mountains became drier and were subject to periodic severe droughts. Habitat changes give some species the edge and give others the axe. We need not choose between climate and hunters. Both impinged on the animals and both must have had an effect. A plausible scenario is that climate and habitat changes depleted the populations and human hunters delivered the coup de grace. Human hunting wouldn't have affected all species equally, and it may have had a role in the recent rapid evolution of bison. Bison antiquus was still here when the human hunters came, but it seems to have disappeared within one or two thousand years of their arrival. One possible explanation is that B. occidentalis and its successor species, B. bison, dealt with the new hunters more effectively than did B. antiquus. Human hunters had a new killing technology-the bladed spear-that enabled them to deliver a mortal wound without coming within reach of mammoth tusks, horse hooves, or bison horns. The long, hooked shape and forward orientation of B. antiquus's horns suggest it may often have dealt with predators by standing its ground and fighting. Stand and fight was a much riskier strategy with the new predator: those who lived by it were likely to die by the spear. The new technology made running away, as B. bison usually does and as B. occidentalis may have done, a better tactic. At the same time, another predator's tactics also favored rapid retreat. As the other large grassland predators dwindled, gray wolves became the largest of those left on the plains. Though they were among the smallest

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of the original suite of plains predators, their strategy of hunting in packs could overcome an individual defense and made rapid retreat the most effective strategy. We'll never know for sure, but it's likely wolves killed more bison than humans hunting on foot and so were the primary predator that shaped B. bison behavior. In any case, since rapid retreat was also the best strategy against spear-throwing and, later, arrow-shooting humans, new antipredator tactics probably were important parts of the bison phylogenetic line's adaptation to new realities on the Great Plains.

MODERN RELATIVES

While bison in North America were moving from the steppe to the central grasslands, bison in Asia and Europe were withdrawing from the steppe to forest, becoming again adapted to forest edge and meadow. Today's descendant of that line is B. bonasus, the European bison. You can tell at a glance that B. bonasus browses more than does B. bison. B. bison's face is nearly perpendicular to the plane of the ground it walks on. It scarcely has to bend its neck to graze grass, but must strain a bit to lift its mouth to the right height and angle to clip leaves from a branch four or five feet above ground. The heads of European bison are set on their necks differently than those of their American relatives. The nose is further forward than the forehead when the neck is in neutral. It's easier for them to browse, but harder for them to graze. They're rangier than B. bison, and while their bodies have less hair, their tails have more. Their horns point forward through the plane of their faces as do the horns of all bison except B. occidentalis and B. bison. Forward-projecting horns facilitate fighting in the manner of domestic cattle-standing close and hooking. Straight-up horns facilitate the running charge, slam-heads-together fighting style of B. bison. The two species are different enough that it's surprising to learn that they interbreed readily, producing perfectly fertile hybrids. In fact, the ease of interbreeding has created a conservation challenge. Some European bison were deliberately interbred with American bison to "refresh the blood" of tiny groups of European bison isolated in zoos. That genetic contamination has precluded using some of those zoo lines to increase

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the genetic diversity of the only free-ranging population, the several hundred bison in Poland's Bialowieza Forest. In North America, B. bison may, or may not, have subdivided, splitting into a subspecies adapted to northern sedge meadow, B. bison athabascae (wood bison), and the more numerous group adapted to the Great Plains, B. bison bison (plains bison). Subspecies are a touchy taxonomic issue. By definition they are fully interfertile with one another; but if they are consistently different, especially qualitatively different (e.g., in color of feathers, shape of horns, distribution of hair), then underlying genetic differences are implied and subspecific status seems justified. Early observers described a different-looking bison living in the boreal forest of northern Canada and called them wood bison. A population of wood bison persisted through the near extinction of the plains bison. Wood Buffalo Park was created to protect them in about 5,000 square miles of boreal forest and sedge meadows well north of Edmonton. This population lived isolated in the northern part of Wood Buffalo Park until plains bison, their numbers grown beyond their pastures elsewhere in Canada, were introduced into the southern part of the park. The two populations mixed, and it appeared that there was no longer a pure line of wood bison. Then a small herd-just eighteen individuals-was discovered to the north. Some suspiciously well-worn trails connected the two areas, but the Canadian government finally concluded the herd was pure wood bison. It moved the herd further north, out of reach of the "hybrids," and nurtured the population, which has expanded well beyond a thousand individuals. Even so, it's not clear that we have two subspecies in North America today. Supporters of subspecific status point to several ways in which wood and plains bison differ. Wood bison, they say, are taller and have more hair on their rumps and less on their shoulders and forelegs. Their hump descends smoothly both fore and aft from its highest point; in contrast, a plains bison's hump descends smoothly to the rear from its highest point, but dips and then rises again just a little as it descends forward to the neck. These taxonomists assert that the differences, though modest, are big and consistent enough. The differences are there. I've seen them-taken photos. But there are some problems with this classification. The decision whether or not the differences between two sets of animals of one species

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are big enough to made them separate species is necessarily somewhat arbitrary, but everyone agrees that the differences must be genetically based. When geneticists look closely at the genes, using current technology to compare the blood types and the tiny sample of the DNA that are available, the genetic distance between woods and plains bison herds is small and not highly reliable. It is still possible there are substantial genetic differences not yet visible to the current genetic technology, but these results make that appear less likely. The biologist Valerius Geist argues that the differences we see are deceiving. He says that rather than being genetic, they are the result of growing up in different environments. Thus, he says, the two "subspecies" are merely ecotypes. Many knowledgeable people don't agree. The issue is still open, and we're left with several possibilities: (1) Perhaps they were and are distinct enough to be subspecies. (2) Perhaps they once were but no longer are distinct. (After all, there were those suspiciously well-worn trails leading from the "hybrid" part of Wood Buffalo Park to the "isolated" wood bison population.) (3) Perhaps they never were distinct-at least not at the genetic level. However the subspecies subplot is resolved, the major story line of the bison's last million years won't change. That is pretty well known and largely clear. And, until horses and hide hunters nearly ended it, it was an inspiring story. It's the story of a small, not particularly prepossessing member of the cow family that conquered the north's rigors, not only adapting to new challenges on a new continent but also becoming the dominant animal and a keystone species in North America's biggest biome. It's a Horatio Alger story for the ages. And the bison did all this while flouting Horace Greeley's advice: they went east.

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CHAPTER 8

How Many?

The Bison Population in Primitive America

There was a long silence-a shocked silence, it turned out-on the other end of the line. "Thirty million? But Dr. Lott, we've always understood there were sixty million." A National Geographic researcher had called to hear my comments on a soon-to-be-published graph depicting the decline of the buffalo but was startled when I said the starting point of the graph was at least twice too high. "My editor isn't going to want to take your word for that. Can you suggest some references we could check?" Sure, I said, call Jim Shaw. They did, and when the graph appeared, its starting point was 30 million. Publishing that number went beyond good research: it was an act of courage. Signs in parks and refuges, informational handouts, history books, newspapers-everywhere you look you get the same story: 60 million bison in primitive North America and as few as a thousand twenty years after the end of the Civil War. Knowing how many there were goes far beyond casual curiosity. We can't understand the ecosystem of primitive North America, or the magnitude of the human rearrangement of that ecosystem, without a good estimate of primitive North America's bison population (see map 1). The available approaches are historical accounts and estimates of the maximum carrying capacity of the North American central grasslands. But it is terribly hard to get good numbers from either. "Sixty million bison" has long been as close to religious dogma as a secular society's beliefs can be. At one time I presented it as gospel myself. Our faith in its reality is an important part of our view of our environmental and social history, and it has been used to quantify our ancestors' stewardship of the land they colonized. Such importance justifies a really close look at how that figure got fixed in our collective consciousness.

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IN SEARCH OF THE 60 MILLION

Jim Shaw has traced the figure of 60 million back to the writings of Earnest Thomas Setoll, ~he great naturalist, and to Seton's source-Colonel Richard 1. Dodge. Colonel Dodge, like his father and his father's father, was a career army officer. He'd been assigned to Kansas in 1869 and commanded Fort Dodge in 1872-73. In 1871 he took a trip along the Arkansas River in a light wagon. The total of 60 million has its foundation in how he described that trip. Dodge said twenty-five miles of his thirty-four-mile trip passed through a herd traveling perpendicular to his route. Seton, or rather his four-volume Lives of Game Anirnals, was sitting on my bookshelves. The flyleaf of each volume is inscribed "Robert S. Norton"-my mother's father. I don't know when the book came into his hands, but it was published in 1927, four years before he became superintendent of the National Bison Range. I inherited it a quarter century ago. The 1927 work contained Seton's second effort to calculate the primitive America bison population. In a 1910 book he had started with an estimate of Dodge's herd that WilHam Hornaday had published in 1887. Seventeen years later he started from scratch. When I was a boy in Montana, a jiggerhead was not a figurehead; it was someone with a head for figures. Seton was a figgerhead. Seton tried every reasonable way to estimate the number of bison in North America before the great slaughter. He read historical accounts of expeditions crossing the plains and prairies before the hide hunt. He determined as best he could the number of hides that had been shipped east by train during the slaughter; he tried to estimate how many bison the continent could feed. But in the end he fell back on the numbers he developed from Dodge's published account of his wagon ride. Seton assumed a herd would travel twenty miles in a day, and as Dodge was in the herd most of the day he calculated that the herd Dodge traveled through was a rectangle twenty-five miles by at least twenty miles. He noted that buffalo could be as dense as twenty-five to the acre in large herds. I don't know how he discovered that, but to picture that

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